Patent Publication Number: US-2015060348-A1

Title: Hollow-fiber membrane module, method for manufacturing hollow-fiber membrane module, and hollow-fiber membrane unit equipped with hollow-fiber membrane module

Description:
TECHNICAL FIELD 
     The present invention relates to a hollow-fiber membrane module, a method for manufacturing a hollow-fiber membrane module, and a hollow-fiber membrane unit equipped with a hollow-fiber membrane module. 
     BACKGROUND ART 
     Hitherto, a hollow-fiber membrane unit has been known in which a plurality of hollow-fiber membrane modules are arranged (for example, Patent Document 1). This hollow-fiber membrane module is formed by stacking a hollow-fiber membrane sheet formed by arranging a hollow-fiber membrane in a sheet shape and liquid-tightly fixing this stacked body to an elongated case using a fixing resin (potting resin). In addition, the end part of the hollow-fiber membrane is open and the hollow-fiber membrane communicates with the internal space of the case. 
     In such a hollow-fiber membrane module, the water to be treated on the primary side (water to be treated side) of the hollow-fiber membrane is filtered under reduced pressure inside the hollow-fiber membrane and the treated water is allowed to flow toward the case when a negative pressure is applied to the inside of the case. Thereafter, the treated water that filtered through a hollow-fiber membrane is discharged toward the device provided on the secondary side (treated water side) of the hollow-fiber membrane module through the water intake port provided in the case. 
     Moreover, an air diffuser for physically washing the hollow-fiber membrane is provided downward the hollow-fiber membrane module. The air is blown into the water to be treated by the air diffuser and the bubble thus generated hits the hollow-fiber membrane, thereby physically washing the hollow-fiber membrane. Furthermore, in the hollow-fiber membrane unit formed by arranging a plurality of hollow-fiber membrane modules, a gap is provided between the hollow-fiber membrane modules so that the bubbles from the air diffuser are able to penetrate between the hollow-fiber membrane modules. 
     In addition, a hollow-fiber membrane module hitherto has been known in which a water collecting member for collecting the filtered water is coupled to the end part of the hollow-fiber membranes arranged in a sheet shape. This hollow-fiber membrane module is constituted such that the water to be treated surrounding the hollow-fiber membrane is sucked into the hollow-fiber membrane and filtered when a negative pressure is generated in the water collecting member and the hollow-fiber membrane from the downstream side (filtered water side) of the water collecting member. In addition, washing of such a hollow-fiber membrane module is performed such that the a washing liquid is allowed to flow from the filtered water side to the water to be treated side when a positive pressure is generated in the water collecting member and the hollow-fiber membrane from the filtered water side of the water collecting member and thus contaminants adhered on the surface and inside fine pores of the hollow-fiber membrane are desorbed from the hollow-fiber membrane. In the hollow-fiber membrane module described in these documents, there is a case in which a pressure difference of several hundred kPa is generated inside the hollow-fiber membrane module, particularly inside the water collecting member at the time of the filtration treatment and the washing treatment of the hollow-fiber membrane module, and it is desired to extend the product life cycle by enhancing the pressure resistant performance of the water collecting member in order to increase the filtering capacity of the hollow-fiber membrane module or depending on the use application of the hollow-fiber membrane module. Moreover, as the structure to increase the pressure resistant performance of the hollow-fiber membrane module, it has been known that a material excellent in the substrate strength is used, a structure able to enhance the adhesive strength with a sealant is used, or a cushioning material is provided at the interface between the machinery and the sealant (for example, Patent Documents 2 to 4). 
     In addition, a hollow-fiber membrane module hitherto has been known in which the end part of the bundle formed by bundling the hollow-fiber membranes is fixed to the housing using a fixing resin. This hollow-fiber membrane module is constituted such that the water filtered through the hollow-fiber membrane is introduced into the housing and collected toward the downstream side through the water collecting passage in the housing (for example, patent document 4). In this patent document 1, when manufacturing the flat type hollow-fiber membrane module, the bundle (stacked body) of the hollow-fiber membrane and the housing (water collecting member) are fixed such that the end part of the hollow-fiber membrane is cut to expose the opening to the end face and the fixing resin is injected into the housing in the state of holding the bundle of the hollow-fiber membranes in the housing and fixed. 
     CITATION LIST 
     Patent Document 
     Patent Document 1: WO 2010/098089 A 
     Patent Document 2: JP 2008-142583 A 
     Patent Document 3: JP 2009-195844 A 
     Patent Document 4: JP 2006-61816 A 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     However, in general, it is preferable that the amount of treated water per unit volume of the hollow-fiber membrane module constituting the hollow-fiber membrane unit determined by the membrane area per unit volume and the permeation rate of the water to be treated is great in order to prevent an increase in size of the hollow-fiber membrane unit. Hence, it is preferable to increase the membrane area per unit volume and the permeation rate. However, the hollow-fiber membrane is too dense when the membrane area per unit volume is excessively increased and thus the washing effect of aeration by the air diffuser decreases. In addition, the physical washing of the hollow-fiber membrane may not be sufficiently performed for this reason. As a result, the hollow-fiber membrane is clogged and the permeation rate of water to be treated decreases. Consequently, there is a problem that only a simple increase in the membrane area per unit volume may not lead to an increase in the amount of treated water per unit volume. 
     In view of such a circumstance, the invention has been achieved firstly to solve the problem described above and an object thereof is to provide a hollow-fiber membrane unit in which a decrease in the permeation rate of the membrane can be prevented by increasing the washing efficiency of the hollow-fiber membrane module and the amount of treated water can be increased by properly adjusting the membrane area per unit volume, and a hollow-fiber membrane module usable in such a hollow-fiber membrane module. 
     In addition, in the structure described in Patent Document 2, it is required to mix a reinforcing agent with the substrate or to use a special material and thus it is not possible to use a water collecting member formed of a reinforcing agent or a material which is not resistant to the substances contained in the water to be treated, as a result, there is a problem that the degree of freedom of the use application of the hollow-fiber membrane module is low. Moreover, in the structure described in Patent Documents 3 and 4, the structure is complicated in order to improve the strength, and the hollow-fiber membrane module is increased in size in order to secure the space for disposing the reinforcing structure, and thus there is a restriction on the structural design of the hollow-fiber membrane module. Furthermore, the improvement in pressure resistant performance is limited depending on the structure of the membrane module, and thus a sufficient function may not be exerted in some cases. 
     In view of such a circumstance, the invention has been achieved secondly to solve the problem described above and another object thereof is to provide a hollow-fiber membrane module of which the use application is not limited and in which the pressure resistant strength of the hollow-fiber membrane module can be improved by a simple structure. 
     In addition, the fixing resin (potting resin) is injected into the housing while holding the bundle in the housing in the method for manufacturing a flat type hollow-fiber membrane module which has been used in the related art. The fixing resin does not sufficiently spread through unless there is a certain space between the hollow-fiber membranes constituting the bundle and thus defective sealing between the hollow-fiber membranes occurs when a flat type hollow-fiber membrane module is manufactured using such a method. Hence, in the method for manufacturing a flat type hollow-fiber membrane module which has been used in the related art, there is a problem that it is impossible to manufacture a flat type hollow-fiber membrane module having a high packing density of the hollow-fiber membrane. 
     Moreover, in the method for manufacturing a flat type hollow-fiber membrane module which has been used in the related art, it is required to use a fixing resin having a relatively low viscosity and a slow cure rate since it is necessary to maintain the sufficient fluidity of the fixing resin until the fixing resin is injected at one or plural locations and spreads through between the hollow-fiber membranes and thus an increase in the cure rate (that is, shortening of time for potting processing) of the fixing resin is limited. 
     In view of such a circumstance, the invention has been achieved thirdly to solve the problem described above and still another object thereof is to provide a method for manufacturing a hollow-fiber membrane module in which the packing density of the hollow-fiber membrane can be increased and which can be manufactured in a short time, and a hollow-fiber membrane module manufactured by such a method. 
     Means for Solving Problem 
     According to the experiment conducted by the inventors or the like, it has been demonstrated that the membrane area per unit volume is properly adjusted when a width of the case is 20 mm or less and the proportion occupied by the total area of the cross-section of the hollow-fiber membrane on one surface having an opening part formed thereon is at least 45%, and thus the amount of water treated by the hollow-fiber membrane module can be increased. 
     Consequently, in order to solve the first problem described above, the invention is a hollow-fiber membrane module which includes a hollow-fiber membrane sheet formed by arranging a hollow-fiber membrane arranged in a sheet shape or a stacked body thereof and a case-shaped water collecting member holding the hollow-fiber membrane sheet or the stacked body thereof, and in which one surface of the water collecting member is filled with a fixing resin (potting resin) and has an opening part for fixing the hollow-fiber membrane sheet stacked body formed thereon, the case has a thickness of 20 mm or less along an out-of-plane direction of the hollow-fiber membrane sheet, and a proportion of a total area of a cross-section of a hollow-fiber membrane of the one surface having an opening part formed thereon is at least 45%. 
     According to the invention having such a configuration, it is possible to have a thickness of the case of the hollow-fiber membrane module of 20 mm or less and a proportion occupied by a total area of a cross-section of a hollow-fiber membrane on the one surface having an opening part formed thereon of at least 45%, and this makes it possible to properly adjust the membrane area per unit volume and thus to increase the amount of water treated by the hollow-fiber membrane module. 
     In this case, it is preferable that the water collecting member has a water collecting path to collect treated water filtered through the hollow-fiber membrane, and a water intake port. 
     In addition, in the invention, the water collecting member is preferably equipped with a means for causing the compressive deformation of the hollow-fiber membrane in the radial direction thereof. 
     According to the invention having such a configuration, it is possible to narrow the cross-section of the hollow-fiber membrane. Moreover, it is possible to sufficiently secure the proportion occupied by the total area of the cross-section of the hollow-fiber membrane even if the width of the case is decreased by narrowing the cross-section of the hollow-fiber membrane. 
     In this case, the means for causing compressive deformation is preferably a pair of convex parts formed on facing inner walls of the water collecting member. 
     In addition, in the invention, the water intake port is preferably in an elliptical shape having a minor axis extending in the out-of-plane direction of the hollow-fiber membrane sheet. 
     According to the invention having such a configuration, it is possible to secure a water intake port having a sufficient size even if the water collecting member (case) is thin. 
     In addition, in the invention, it is preferable that the water intake port is formed on at least one end face of the water collecting member, and a thick wall part having a thickened thickness in the out-of-plane direction of the hollow-fiber membrane sheet of the water collecting member is equipped on the at least one end face of the water collecting member having a water intake port formed thereon. 
     According to the invention having such a configuration, it is possible to secure the area for forming the water intake port by widening the width of the end part at which a water intake port is formed. 
     In addition, in the invention, the water collecting member has a reinforcing structure formed by thickening the side wall of the water collecting member in the out-of-plane direction of the hollow-fiber membrane sheet. 
     According to the invention having such a configuration, it is possible to secure the rigidity of the case by the reinforcing structure even when the case is thin. 
     In addition, according to the experiment conducted by the inventors or the like, it has been demonstrated that it is possible to expose the hollow-fiber membrane to a great quantity of air from the air diffuser and thus to improve the washing efficiency when the thickness of the side wall of the case in the width direction of the hollow-fiber membrane module is 2 mm or less. 
     Consequently, in the invention, the thickness of the side wall of the water collecting member in the out-of-plane direction of the hollow-fiber membrane sheet is preferably 2 mm or less. 
     According to the invention having such a configuration, it is possible to expose the hollow-fiber membrane to a great quantity of air from the air diffuser and thus to improve the washing efficiency. 
     In addition, according to the experiment conducted by the inventors or the like, it has been demonstrated that it is possible to further increase the physical washing efficiency of the hollow-fiber membrane when the hollow-fiber membrane modules are arranged at an interval of 3 mm or more and 15 mm or less in the hollow-fiber membrane unit using the hollow-fiber membrane module described above. 
     Consequently, in the invention, it is preferable that the hollow-fiber membrane unit is formed by arranging a plurality of the hollow-fiber membrane modules described above and the plurality of the hollow-fiber membrane modules are arranged at an interval of 3 mm or more and 15 mm or less. 
     According to the invention having such a configuration, it is possible to further increase the physical washing efficiency of the hollow-fiber membrane. 
     In this case, it is preferable that the thick wall part of the hollow-fiber membrane module is dimensioned so as to be in contact with the thick wall part of the adjacent hollow-fiber membrane module, and the reinforcing structure of the hollow-fiber membrane module is dimensioned so as to be in contact with the reinforcing structure of the adjacent hollow-fiber membrane module. 
     According to the invention having such a configuration, it is possible to allow the thick wall part and the reinforcing structure to function as a spacer between the adjacent hollow-fiber membrane modules and thus to properly maintain the width between the hollow-fiber membrane modules. 
     In addition, in the invention, a collective water intake pipe which couples two or more adjacent hollow-fiber membrane modules and communicates with all water intake ports of the coupled two or more hollow-fiber membrane modules is preferably included. 
     According to the invention having such a configuration, it is possible to collect the treated water filtered by the collective water intake pipe, and this makes it possible to decrease the number of components. 
     In addition, in the invention, a seal member which is disposed between the collective water intake pipe and the hollow-fiber membrane modules and surrounds the water intake ports is preferably included. 
     According to the invention having such a configuration, it is possible to securely seal the space between the collective water intake pipe and the water intake ports of the hollow-fiber membrane modules. 
     In this case, it is preferable that the membrane area per volume of the hollow-fiber membrane is preferably from 100 to 1000 m 2 /m 3 . 
     In addition, in order to solve the second problem described above, the invention is a hollow-fiber membrane module which includes a hollow-fiber membrane sheet formed by arranging a plurality of hollow-fiber membranes having at least one open end part in a sheet shape or a stacked body thereof and a water collecting member holding the hollow-fiber membrane sheet or the stacked body thereof, and in which the hollow-fiber membrane sheet or the stacked body thereof is liquid tightly fixed to the water collecting member using a fixing resin (potting resin) and the water collecting member is equipped with a water collecting channel communicating with an opening of the hollow-fiber membrane and extending in an arrangement direction of the hollow-fiber membranes, a pair of side walls extending in a longitudinal direction of the water collecting member, and a columnar body coupling the pair of side walls with each other in the water collecting channel. 
     According to the invention having such a configuration, it is possible to reinforce the water collecting member by coupling the pair of side walls of the water collecting member by the columnar body. Moreover, this makes it possible to improve the pressure resistant strength of the water collecting member with respect to the positive pressure and negative pressure generated in the inside of the water collecting member. It is possible to form the water collecting member using various materials since this columnar body has a simple structure. Furthermore, it is possible to adopt the module without restrictions on the use application thereof since a reinforcing agent (adhesive) or the like is not required. 
     In addition, in the invention, the cross-sectional shape perpendicular to the axis of the columnar body preferably has a streamlined section. 
     According to the invention having such a configuration, it is possible to decrease the resistance force to the flow of filtered water even if the filtered water flowing inside the water collecting member hits the columnar body since the columnar body has a streamlined section. 
     In addition, in the invention, it is preferable that the water collecting member has a water intake port for taking out the filtered water from the hollow-fiber membrane module formed thereon and is equipped with the plurality of columnar bodies, these columnar bodies are arranged in an extended longitudinal direction of the water collecting member, and the cross-sectional area perpendicular to the axis when the plurality of columnar bodies are viewed from the longitudinal direction decreases as a distance of the columnar body from the water intake port decreases. 
     According to the invention having such a configuration, it is possible to decrease the projected area when the plurality of columnar bodies are viewed from the longitudinal direction of the water collecting member as the distance of the columnar body from the water intake port decreases, and this makes it possible to decrease the resistance force to the flow of filtered water in the vicinity of the water intake port. 
     In addition, in the invention, the columnar body is preferably integrally molded with the water collecting member. 
     It is possible to enhance the bonding strength between the reinforcing structure and the water collecting member by having such a configuration in which the columnar body is integrally molded with the water collecting member, and thus the pressure resistant strength of the water collecting member is further increased. 
     In addition, in the invention, it is preferable that the water collecting member is formed by bonding a first member having one of the pair of side walls and a second member having the other of the side walls, and the columnar body is formed on either the first member or the second member and weld bonded to the other. 
     In addition, in order to solve the third problem described above, the invention is a method for manufacturing a hollow-fiber membrane module having a hollow-fiber membrane sheet stacked body constituted by stacking a plurality of hollow-fiber membrane sheets formed by arranging and binding a great number of hollow-fiber membranes, which is configured such that a stacked body of hollow-fiber membrane sheets is formed by performing a process of coating a liquid resin composition on a vicinity of the side having the tip of the hollow-fiber membrane arranged thereon of the hollow-fiber membrane sheet and a process of stacking a hollow-fiber membrane sheet on this hollow-fiber membrane sheet by the adhesion of the liquid resin composition a plurality of times and the hollow-fiber membrane stacked body is attached to a water collecting member. 
     According to the invention having such a configuration, it is possible to firmly spread the fixing resin between the hollow-fiber membrane sheets by performing the process of coating a fixing resin on the vicinity of the side having the tip of the hollow-fiber membrane arranged thereon of the hollow-fiber membrane sheet and stacking a hollow-fiber membrane sheet on this. Moreover, it is not required to consider the interval between the hollow-fiber membrane sheets since the fixing resin can be directly coated on the hollow-fiber membrane sheet, and thus it is possible to minimize the interval between the hollow-fiber membrane sheets. This makes it possible to manufacture a hollow-fiber membrane module having hollow-fiber membranes arranged at a high packing density. Furthermore, it is possible to use a fixing resin having a relatively fast cure rate since it is not required to consider the time to allow the fixing resin to spread through between the hollow-fiber membranes by sequentially stacking the hollow-fiber membrane sheets on the hollow-fiber membrane sheet coated with a fixing resin. This makes it possible to shorten the time to fabricate a hollow-fiber membrane stacked body. 
     In addition, in the invention, it is preferable that the water collecting member is equipped with an opening part for receiving the hollow-fiber membrane stacked body, a pair of side walls which extends from this opening part and to which the hollow-fiber membrane stacked body received through the opening part is fixed, a water collecting passage which is formed on a side opposite to the opening part with respect to the pair of side walls and collects water purified by the hollow-fiber membrane sheet, and a water collecting port communicating with this water collecting passage, the water collecting member is formed by bonding a first member including at least one side wall of the pair of side walls with a second member including at least the other side wall, and the second member is attached to the first member and the hollow-fiber membrane stacked body after attaching the hollow-fiber membrane stacked body to the first member in the process of attaching the hollow-fiber membrane stacked body to a water collecting member. 
     According to the invention having such a configuration, the water collecting member can have a two-division structure of the first member and the second member. This makes it possible to easily provide a protruding part for reinforcing the adhesion with the fixing resin on the side wall in the case of forming a water collecting member by injection molding. 
     In addition, in order to solve the third problem described above, the invention is a method for manufacturing a hollow-fiber membrane module equipped with a hollow-fiber membrane stacked body constituted by stacking a plurality of hollow-fiber membrane sheets formed by arranging and binding a great number of hollow-fiber membranes in a sheet shape and a water collecting member for collecting water purified by the hollow-fiber membrane stacked body. In the method, the water collecting member is equipped with an opening part for receiving the hollow-fiber membrane stacked body, a pair of side walls which extends from the opening part and to which the hollow-fiber membrane stacked body received through the opening part is fixed, a water collecting passage which is formed on a side opposite to the opening part with respect to this pair of side walls and collects water purified by the hollow-fiber membrane sheet, and a water collecting port communicating with this water collecting passage, and formed by bonding a first member including at least one side wall of the pair of side walls with a second member including at least the other side wall. The method includes a process of coating a liquid resin composition on the side wall of the first member, a process of stacking a vicinity of a side having an end of a hollow-fiber membrane arranged thereon of the hollow-fiber membrane sheet on the side wall of the first member coated with a liquid resin composition, a process of coating a liquid resin composition on the vicinity of a side having an end of a hollow-fiber membrane arranged thereon of the hollow-fiber membrane sheet stacked on the side wall of the first member and stacking a hollow-fiber membrane sheet having the same shape as this hollow-fiber membrane sheet thereon, a process of performing a process of coating a liquid resin composition on the vicinity of a side having an end of a hollow-fiber membrane arranged thereon of the hollow-fiber membrane sheet previously stacked and stacking a hollow-fiber membrane sheet having the same shape as this hollow-fiber membrane sheet thereon one or more times, a process of coating a liquid resin composition on the vicinity of a side having an end of a hollow-fiber membrane arranged thereon of the hollow-fiber membrane sheet previously stacked, and a process of bonding the second member to the first member so as to sandwich the hollow-fiber membrane stacked body disposed on the side wall of the first member between the first member and the second member, and attaching to the hollow-fiber membrane stacked body. 
     According to the invention having such a configuration, it is possible to firmly spread the fixing resin between the hollow-fiber membrane sheets by performing the process of coating a fixing resin on the vicinity of the side having the end of the hollow-fiber membrane arranged thereon of the hollow-fiber membrane sheet and stacking a hollow-fiber membrane sheet having the same shape as this hollow-fiber membrane sheet thereon one or more times. Moreover, it is not required to consider the interval between the hollow-fiber membrane sheets since the fixing resin can be directly coated on the hollow-fiber membrane sheet, and thus it is possible to minimize the interval between the hollow-fiber membrane sheets. This makes it possible to manufacture a hollow-fiber membrane module having hollow-fiber membranes arranged at a high packing density. Furthermore, it is possible to use a fixing resin having a relatively fast cure rate since it is not required to consider the time to allow the fixing resin to spread through between the hollow-fiber membranes by sequentially stacking the hollow-fiber membrane sheets on the hollow-fiber membrane sheet coated with a fixing resin. In addition, it is also possible to eliminate the process of cutting the end part of the hollow-fiber membrane stacked body. These make it possible to shorten the time to fabricate a hollow-fiber membrane stacked body. 
     In addition, in the invention, the process of forming a hollow-fiber membrane stacked body by stacking a hollow-fiber membrane sheet is preferably performed at least in the state in which the hollow-fiber membrane in the vicinity of the side to be coated with a fixing resin is arranged in the horizontal direction. 
     In addition, in the invention, the first member and the second member are preferably bonded by either bonding by welding or bonding by an adhesive resin. 
     In addition, in the invention, the process of attaching the hollow-fiber membrane stacked body to the water collecting member preferably includes a process of disposing a seal member between the first member and the second member. 
     In addition, in the invention, bonding of the first member with the second member is preferably performed by the pressing force of the first member by the second member. 
     In addition, in the invention, the viscosity of the liquid resin composition is preferably from 10,000 to 50,000 mPa·s. 
     In addition, in the invention, the liquid resin composition preferably includes a urethane resin or an epoxy resin as a main constituent. 
     In addition, in the invention, it is preferable that a protruding part for bonding the side wall of the first member and the side wall of the second member is formed at least one location of the water collecting passage, and the side wall of the first member and the second member are bonded via the protruding part. 
     In addition, in order to solve the third problem described above, the invention is a method for manufacturing a hollow-fiber membrane module equipped with one sheet of hollow-fiber membrane sheet formed by arranging and binding a great number of hollow-fiber membranes, which includes a process of coating a liquid resin composition on a vicinity of a side having a tip of a hollow-fiber membrane arranged thereon of a hollow-fiber membrane sheet and a process of attaching this hollow-fiber membrane stacked body to a water collecting member. 
     Effect of the Invention 
     According to the invention, it is possible to solve the third problem that a decrease in the permeation rate of the membrane can be prevented by increasing the washing efficiency of the hollow-fiber membrane module and the amount of treated water can be increased by properly adjusting the membrane area per unit volume as described above. 
     In addition, according to the invention, it is possible to solve the second problem that the use application of the hollow-fiber membrane module is not limited and the pressure resistant strength thereof can be improved by a simple structure as described above. 
     In addition, according to the invention, it is possible to solve the first problem that the packing density of the hollow-fiber membrane can be increased and the hollow-fiber membrane module can be manufactured in a short time as described above. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a hollow-fiber membrane unit equipped with a hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 2  is a cross-sectional view of the II-II′cross-section of  FIG. 1 ; 
         FIG. 3  is a trihedral figure of a hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 4  is an enlarged perspective view of a part of a hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 5  is a cross-sectional view of a cross-section in a horizontal direction of a hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 6  is a cross-sectional view of the VI-VI′ cross-section of  FIG. 4 ; 
         FIG. 7  is a cross-sectional view of the VII-VII′ cross-section of  FIG. 6 ; 
         FIG. 8  is a cross-sectional view of the VIII-VIII′ cross-section of  FIG. 6 ; 
         FIG. 9  is a perspective view illustrating a collective water intake pipe of a hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 10  is an enlarged cross-sectional view of a part of a hollow-fiber membrane module according to an embodiment of the invention and a cross-sectional view of the X-X cross-section of  FIG. 9 ; 
         FIG. 11  is a graph illustrating a result of a differential pressure test of a hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 12  is a graph illustrating a result of a differential pressure test of a hollow-fiber membrane module according to Comparative Example; 
         FIG. 13  is a perspective view of a hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 14  is a cross-sectional view of the XIV-XIV′ cross-section of a hollow-fiber membrane module illustrated in  FIG. 13 ; 
         FIG. 15  is a cross-sectional view of the XV-XV′ cross-section of a hollow-fiber membrane module illustrated in  FIG. 13 ; 
         FIG. 16  is a perspective view illustrating a flat type hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 17  is a cross-sectional view illustrating a cross-section of a water collecting member according to an embodiment of the invention; 
         FIG. 18  is a plan view illustrating a hollow-fiber membrane sheet of a flat type hollow-fiber membrane module according to an embodiment of the invention; 
         FIG. 19  is a perspective view illustrating a manufacturing process of a flat type hollow-fiber membrane module according to an embodiment of the invention; and 
         FIG. 20  is a perspective view illustrating a part of a flat type hollow-fiber membrane module according to a modified example of an embodiment of the invention. 
     
    
    
     BEST MODE(S) FOR CARRYING OUT THE INVENTION 
     Hereinafter, a hollow-fiber membrane module according to a first embodiment of the invention will be described with reference to the drawings.  FIG. 1  is a perspective view of a hollow-fiber membrane unit, and  FIG. 2  is a cross-sectional view of the II-II′ cross-section. 
     First, as illustrated in  FIGS. 1 and 2 , a hollow-fiber membrane unit  101  includes a plurality of hollow-fiber membrane modules  103  arranged in a constant direction and a holding structure  105  for holding the hollow-fiber membrane module  103  at a predetermined position by holding the upper part and lower part of the hollow-fiber membrane module  103 . In addition, an air diffuser  107  for performing aeration is provided at the lower part of the hollow-fiber membrane module  103  arranged. 
     The plurality of hollow-fiber membrane modules  103  are arranged at a constant interval by the holding structure  105 . Moreover, a diffuser pipe  109  of the air diffuser  107  is positioned at the lower part of the interval of the hollow-fiber membrane module  103  arranged so that the air come out from the diffuser pipe  109  rises and penetrates between the hollow-fiber membrane modules  103 . 
       FIG. 3  is the trihedral figure of the hollow-fiber membrane module. The hollow-fiber membrane module  103  includes a hollow-fiber membrane sheet stacked body  113  formed by stacking a hollow-fiber membrane sheet  111  and a pair of cases  115  to fix the hollow-fiber membrane sheet stacked body  113 . The hollow-fiber membrane sheet  111  is formed, for example, by arranging a great number of PVDF hollow-fiber membranes in a sheet shape. Moreover, at least one end part of the hollow-fiber membrane is open so that the treated water that is filtered by passing through the hollow-fiber membrane can be discharged from the open end part. 
     The case  115  for fixing the hollow-fiber membrane sheet stacked body  113  holds the hollow-fiber membrane sheet stacked body  113  at the top and bottom of the hollow-fiber membrane sheet stacked body  113 . In addition, an elliptically shaped water intake port  117  for taking out the treated water that is filtered from the case is formed on the end face of the case  115 . It is possible to secure the opening area of the water intake port  117  while having a small width of the water intake port  117  (the length in the width direction of the case) by adopting an elliptical shape as the shape of the water intake port  117 . 
       FIG. 4  is an enlarged perspective view illustrating the bottom of the hollow-fiber membrane module. 
     As illustrated in  FIG. 4 , the case  115  has an elongated box shape. In addition, an opening for fixation  119  for fixing the hollow-fiber membrane sheet stacked body  113  is formed at the upper part of the case  115 . The inside of the opening for fixation  119  is filled with a fixing resin (potting resin)  121  for fixing the hollow-fiber membrane sheet stacked body  113  to the case  115 , and the hollow-fiber membrane sheet stacked body  113  and the case  115  are liquid tightly sealed by this fixing resin(potting resin)  121 . The length of the opening for fixation  119  is from 200 mm to 1200 mm and preferably from 300 mm to 800 mm, and the width is preferably from 5 to 20 mm in order to maintain the disposition efficiency of the hollow-fiber membrane module  103  and to secure the rigidity to the deformation. Moreover, the thickness of the side wall of the case  115  extending along the opening for fixation  119  is preferably 2 mm or less. It is possible to shorten the distance between the hollow-fiber membrane sheet stacked body  113  fixed in opening for fixation  119  and the flow path of the air from the diffuser pipe  109  formed between the hollow-fiber membrane modules by decreasing the thickness of this side wall. This makes it possible to expose the hollow-fiber membrane sheet stacked body  113  to more air and thus to increase the efficiency of the aeration. Furthermore, it is preferable that the longitudinal direction of the opening for fixation  119  is divided into more than one or a reinforcing member is provided at a predetermined interval in order to enhance the rigidity to the deformation. 
     The basic width D1 (hereinafter, referred to as the “basic width D1”) of the case  115  is 15 mm and preferably 10 mm or less. The case  115  includes a thick wall part  115   a  having a width wider than the basic width D1 at one end or both ends thereof in addition to this. The thick wall part  115   a  is the portion that is thickened to be thicker than the basic width D1 in the out-of-plane direction of the hollow-fiber membrane sheet  111 . This thick wall part  115   a  has the same wall thickness as a part of the case  115  having a basic width D1 and is constituted by expanding the internal space thereof in the out-of-plane direction of the hollow-fiber membrane sheet  111 . The thick wall part  115   a  is formed at the end part of the side provided with the water intake port  117 . This thick wall part  115   a  is a portion of the case  115  having a widened width in order to secure the area in the width direction of the water intake port  117 . Moreover, the thick wall part  115   a  is formed on the side provided with the water intake port  117  and the internal space thereof has a wider width than other portions. This makes it possible to increase the opening area of the water intake port  117  and thus to improve the efficiency of taking out water from the case  115 . Furthermore, the thickness of the thick wall part  115   a  is determined such that the thick wall part  115   a  comes into contact with the thick wall part  115   a  of the adjacent hollow-fiber membrane module  103  when the hollow-fiber membrane modules  103  are arranged. This allows the thick wall part  115   a  to function as a spacer between the hollow-fiber membrane modules  103  when the hollow-fiber membrane modules  103  are arranged. 
     In addition, the case  115  has a reinforcing structure  115   b  for increasing the rigidity thereof. The reinforcing structure  115   b  is formed on a side surface of the case  115  and secures the rigidity of the case  115  thinned. This reinforcing structure  115   b  is fixed to the side surface of the case  115  and is constituted by a relatively hard material having a constant thickness. The wall thickness of the case  115  is substantially increased by fixing the reinforcing structure  115   b  to the side surface of the case  115  and thus it is possible to increase the rigidity thereof. Furthermore, as the reinforcing structure  115   b , those obtained by partly increasing the wall thickness of the case  115  may be used. A plurality of reinforcing structures  115   b  are arranged along the extending direction of the case  115 . Meanwhile, the case  115  may not be provided or may be provided with only one reinforcing structure  115   b  depending on the length thereof. 
     The hollow-fiber membrane sheet stacked body  113  is fixed to the opening for fixation  119  of the case  115  as described above, and the hollow-fiber membrane of the hollow-fiber membrane sheet stacked body  113  is disposed so as to upwardly extend from the upper surface of the case  115 . In addition, in the case of cutting the hollow-fiber membrane sheet stacked body  113  in the horizontal direction, the cut section of the hollow-fiber membrane is exposed to the cut section thereof, but it has been demonstrated that it is possible to increase the amount of treated water by properly adjusting the membrane area per unit volume when the proportion occupied by the total area of the cross-section of the hollow-fiber membrane is at least 45% on the one surface having an opening for fixation formed thereon according to the experiment conducted by the present inventors or the like. In other words, as illustrated in  FIG. 5 , the proportion of the sum of the cross-sectional area of the hollow-fiber membrane and the area of cross-section in the horizontal direction of the hollow-fiber membrane module  103  at an arbitrary position is expressed by Equation: nπr 2 /WL (n represents the number of hollow-fiber membrane) when the width of the opening part for fixation  119  when viewed from the upper surface is denoted as W, the length is denoted as L, and the radius of the hollow-fiber membrane is denoted as r. It is preferable that this proportion is 45% or more and preferably 50% or more. Meanwhile, it is not required to consider the decrease of the area of the cross-section in the horizontal direction of the hollow-fiber membrane module  103  by the thick wall part  115   a  in a case in which the case  115  has a thick wall part  115   a . Meanwhile, the upper limit of the proportion is arbitrarily set depending on the size of the module but is preferably 90% or less and more preferably 85% or less in consideration of the sufficient adhesion and fixation of the hollow-fiber membrane. 
     In addition, the distance between the side wall of the case and the surface of the hollow-fiber membrane sheet stacked body  113  can be relatively short to be 2 mm or less by decreasing the thickness of the wall of the case  115 , and this allows the air risen from the diffuser pipe  109  to easily hit the surface of the hollow-fiber membrane sheet stacked body  113 . Meanwhile, it is more preferable as the distance is shorter, but the distance is preferably 0.5 mm or more in consideration of the contact between the adjacent cases. 
       FIG. 6  is a cross-sectional view of the VI-VI′ cross-section of  FIG. 4 ,  FIG. 7  is a cross-sectional view of the VII-VII′ cross-section of  FIG. 6 , and  FIG. 8  is a cross-sectional view of the VIII-VIII′ cross-section of  FIG. 6 . 
     As illustrated in  FIG. 6 , the upper of the internal space of the case  115  is substantially closed by the fixing resin (potting resin)  121  and the hollow-fiber membrane, a water collecting path  125  for collecting water filtered through the hollow-fiber membrane is formed at the lower of the internal space thereof. Water filtered through the hollow-fiber membrane flows from the opening of the end part to the water collecting path  125  and flows from the water collecting path  125  to the water intake port  117 . 
     In addition, the case  115  includes a compression means for compressing a part of the hollow-fiber membrane. The compression means is a pair of convex parts  127  extending in the extending direction of the case  115  along the inner wall of the case  115 , and the pair of convex parts  127  formed on the facing inner walls are formed at the positions facing each other along the inner wall. The convex part  127  is formed on the portion in contact with the fixing resin (potting resin)  121  embedding the end part of the hollow-fiber membrane of the inner wall of the case  115 . Moreover, the hollow-fiber membrane is not deformed in the cut section at the height at which the convex part  127  is not formed as illustrated in  FIG. 7 . On the other hand the hollow-fiber membrane is pressed by the convex part  127  and thus deformed in the cut section at the height at which the convex part  127  is formed as illustrated in  FIG. 8 . 
     The protrusion quantity of the convex part  127  is appropriately set according to the diameter of the hollow-fiber membrane and the flow quantity of water decreases since the internal space of the hollow-fiber membrane is crushed when the protrusion quantity is too large. Consequently, the protrusion quantity of the convex part  127  is preferably a degree in which the width of the portion of the hollow-fiber membrane located between the pair of convex parts  127  facing each other is reduced by 30%. It is not required to decrease the radius or number of the hollow-fiber membrane even in a case in which the width of the case  115  is narrow as the hollow-fiber membrane is compressed in the case  115  by providing such convex parts  127  and thus it is possible to increase the density of the hollow-fiber membrane. In addition, it is possible to improve the strength of the case  115  by providing the convex part  127  along the inner wall of the case  115 . Furthermore, it is possible to increase the drawing strength of the fixing resin (potting resin)  121  by providing the convex part  127  on the inner wall of the case  115  and allowing the convex part  127  to bite into the fixing resin (potting resin)  121 . It is also possible to form a plurality of convex parts  127  in order to further increase the drawing strength of the fixing resin (potting resin)  121 . 
     In addition, the hollow-fiber membrane unit  101  includes a collective water intake pipe communicating with the plurality of water intake ports  117  of the hollow-fiber membrane module  103  at the same time. 
       FIG. 9  is a perspective view of the collective water intake pipe, and  FIG. 10  is an enlarged cross-sectional view of a part of the hollow-fiber membrane module and a view for describing the attachment state of the collective water intake pipe. 
     As illustrated in  FIG. 9 , a collective water intake pipe  129  includes a body  133  having a plurality of inflow openings  131  formed thereon and a water intake pipe  135  extending from this body  133 . The plurality of inflow openings  131  are arranged at a predetermined interval, and the size and shape of each of the inflow openings  131  correspond to the size and shape of the water intake port  117  of the hollow-fiber membrane module  103 . Moreover, the inflow opening  131  communicates with the water intake pipe  135  inside the outside  133 . The treated water flowed inside the body from the plurality of inflow openings  131  flows into the water intake pipe  135  and then collectively flows to the downstream side (treated water side). 
     In addition, as illustrated in  FIG. 10 , the circumference of the inflow opening  131  is provided with a seal member  137  having an elliptical ring shape so that the space between the inflow opening  131  and the water intake port  117  is sealed by this. Using such a collective water intake pipe  129  makes it possible to collectively take out the treated water from the relatively thin case  115  by a component having a simple structure, and thus it is not required to provide the water intake pipe in accordance with the number of the hollow-fiber membrane module  103 . 
     The hollow-fiber membrane unit  101  includes the plurality of hollow-fiber membrane modules  103  having such a structure as described above, and the respective hollow-fiber membrane modules  103  are arranged at a predetermined interval from each other by the holding structure  105 . The gap between the hollow-fiber membrane modules  103  is provided to allow the air risen from the diffuser pipe  109  to pass through. It is not possible to sufficiently perform the physical washing of the hollow-fiber membrane since the bubbles from the diffuser pipe  109  are not sufficiently penetrates therethrough when this gap is too narrow. On the contrary, the density of the hollow-fiber membrane decreases when the gap is too wide. Consequently, the gap between the hollow-fiber membrane modules  103  is preferably set to 3 mm or more and 15 mm or less. 
     Moreover, according to the experiment conducted by the inventors or the like, it has been demonstrated that it is possible to increase the amount of water treated by the hollow-fiber membrane unit  101  by properly adjusting the membrane area per unit volume when a thickness in the array direction of the hollow-fiber membrane module  103  is 15 mm or less and the proportion occupied by the sum of the cross-section of the hollow-fiber membrane is at least 45% in horizontal cross-section of the location at which the hollow-fiber membrane is fixed to the case  115 , and further the physical washing of the hollow-fiber membrane can be sufficiently performed by arranging such hollow-fiber membrane modules  103  at an interval of 3 mm or more and 15 mm or less. 
     Consequently, according to the hollow-fiber membrane unit  101  described above, it is possible to increase the amount of water treated by the hollow-fiber membrane module which is determined by the membrane area per unit volume and the permeation rate of the water to be treated. 
     Hereinafter, Examples and Comparative Examples of the invention will be described in detail. 
     Example 1 
     Two sheets of the hollow-fiber membrane sheets obtained by aligning 160 pieces of a polyvinylidene fluoride hollow-fiber membrane (nominal pore size: 0.4 μm, outer diameter: 2.8 mm, manufactured by Mitsubishi Rayon Co., Ltd.) in one direction at an effective length of 875 mm was prepared. An ABS case having a thickness of 7.5 mm was prepared as the case. Each of the upper end and lower end of the sheet was fixed to the case using a fixing resin (potting resin) composed of a urethane resin in the state in which two sheets of hollow-fiber membranes having an open upper end and an open lower end are superimposed. The proportion of the sum of the cross-sectional area and the area of the cut section in the horizontal direction of the hollow-fiber membrane of the hollow-fiber membrane module fabricated at this time was 53%. Thereafter, the top and bottom of the hollow-fiber membrane module were fixed such that the hollow-fiber membrane extends in the vertical direction, and the hollow-fiber membrane module was disposed so as to have a gap of the hollow-fiber membrane module of 6 mm, thereby fabricating the hollow-fiber membrane module. 
     Example 2 
     Two sheets of the hollow-fiber membrane sheets obtained by aligning 160 pieces of a polyvinylidene fluoride hollow-fiber membrane (nominal pore size: 0.4 μm, outer diameter: 2.8 mm, manufactured by Mitsubishi Rayon Co., Ltd.) in one direction at an effective length of 875 mm was prepared. An ABS case having a thickness of 7.5 mm was prepared as the case. Thereafter, the convex part having a height of 0.3 mm was formed on the inner wall of the case in two stages. Each of the upper end and lower end of the sheet was fixed to the case using a fixing resin (potting resin) composed of a urethane resin in the state in which two sheets of hollow-fiber membranes having an open upper end and an open lower end are superimposed. The proportion of the sum of the cross-sectional area and the area of the cut section in the horizontal direction of the hollow-fiber membrane of the hollow-fiber membrane module fabricated at this time was 53%. Thereafter, the top and bottom of the hollow-fiber membrane module were fixed such that the hollow-fiber membrane extends in the vertical direction, and the hollow-fiber membrane module was disposed so as to have a gap of the hollow-fiber membrane module of 6 mm, thereby fabricating the hollow-fiber membrane module. 
     Comparative Example 1 
     Five sheets of the hollow-fiber membrane sheets obtained by aligning 160 pieces of a polyvinylidene fluoride hollow-fiber membrane (nominal pore size: 0.4 μm, outer diameter: 2.8 mm, manufactured by Mitsubishi Rayon Co., Ltd.) in one direction at an effective length of 875 mm was prepared. An ABS case having a thickness of 30 mm was prepared as the case. Each of the upper end and lower end of the sheet was fixed to the case using a fixing resin (potting resin) composed of a urethane resin in the state in which five sheets of hollow-fiber membranes having an open upper end and an open lower end are superimposed. The proportion of the sum of the cross-sectional area and the area of the cut section in the horizontal direction of the hollow-fiber membrane of the hollow-fiber membrane module fabricated at this time was 33%. Thereafter, the top and bottom of the hollow-fiber membrane module were fixed such that the hollow-fiber membrane extends in the vertical direction, and the hollow-fiber membrane module was disposed so as to have a gap of the hollow-fiber membrane module of 15 mm, thereby fabricating the hollow-fiber membrane module. 
     Comparative Example 2 
     Two sheets of the hollow-fiber membrane sheets obtained by aligning 160 pieces of a polyvinylidene fluoride hollow-fiber membrane (nominal pore size: 0.4 μm, outer diameter: 2.8 mm, manufactured by Mitsubishi Rayon Co., Ltd.) in one direction at an effective length of 875 mm was prepared. An ABS case having a thickness of 7.5 mm was prepared as the case. Each of the upper end and lower end of the sheet was fixed to the case using a fixing resin (potting resin) composed of a urethane resin in the state in which two sheets of hollow-fiber membranes having an open upper end and an open lower end are superimposed. The proportion of the sum of the cross-sectional area and the area of the cut section in the horizontal direction of the hollow-fiber membrane of the hollow-fiber membrane module fabricated at this time was 53%. Thereafter, the top and bottom of the hollow-fiber membrane module were fixed such that the hollow-fiber membrane extends in the vertical direction, and the hollow-fiber membrane module was disposed so as to have a gap of the hollow-fiber membrane module of 2 mm, thereby fabricating the hollow-fiber membrane module. 
     The test conditions of Examples 1 and 2 and Comparative Examples 1 and 2 are summarized in Table 1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Comparative 
                   
                   
               
               
                   
                 Example 1 
                 Example 1 
                 Example 2 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Outer diameter of 
                 mm 
                 2.8 
                 2.8 
                 2.8 
               
               
                 membrane 
               
               
                 Number of membrane 
                   
                 800 
                 320 
                 320 
               
               
                 Effective length of 
                 mm 
                 875 
                 875 
                 875 
               
               
                 membrane 
               
               
                 Length of membrane fixing 
                 mm 
                 500 
                 500 
                 500 
               
               
                 part 
               
               
                 Thickness of case 
                 mm 
                 26 
                 5.2 
                 5.2 
               
               
                 Height of convex part 
                 mm 
                 — 
                 — 
                 0.3 
               
               
                 Area of membrane 
                 m2 
                 6.2 
                 2.5 
                 2.5 
               
               
                 Proportion of sum of cross- 
                 % 
                 41 
                 76 
                 76 
               
               
                 sectional area and area of 
               
               
                 cut section in horizontal 
               
               
                 direction of hollow-fiber 
               
               
                 membrane 
               
               
                   
               
            
           
         
       
     
     The water permeating performance of the hollow-fiber membrane modules fabricated in (Example 1) and (Example 2) were evaluated under the same conditions. As a result, there was no difference in water permeating performance and a change in the water permeating performance due to the convex shape on the inner wall of the case or the breakage or defect of the hollow-fiber membrane was not confirmed. 
     The hollow-fiber membrane modules fabricated in (Example 1) and (Example 2) were disposed in the same water tank and a comparative test was conducted. The test results are presented in  FIG. 11  and  FIG. 12 . 
     As illustrated in  FIG. 11  and  FIG. 12 , the air diffusion linear velocity per projection floor area of the hollow-fiber membrane module was 230 m/h and the MLSS concentration in the water tank was controlled in the range of from 8,000 to 12,000 mg/L. The hydraulic retention time was 8 hours in the whole system. The filtration linear velocity was changed stepwise, and the change in the differential pressure of membrane filtration at that time was compared. In addition, the hollow-fiber membrane filter fabricated in (Comparative Example 1) was disposed in the same water tank and the comparative test was conducted, but the air diffusion between the hollow-fiber membrane modules was not efficiently performed. 
     In addition, In Example 2, the breakage of the hollow-fiber membrane or the loss of pressure due to the narrowed inside of the hollow-fiber membrane was not observed although the hollow fiber was pressed and deformed by providing a convex part to the inner wall of the case at the thin membrane fixing part, and thus it was possible to increase the strength of the thin part of the case. 
     As can be seen from  FIG. 11  and  FIG. 12 , the differential pressure was stable at the filtration linear velocity of (LV) of 35 LMH but tended to increase at 40 LMH or more in Comparative Examples 1 and 2. On the other hand, the differential pressure was stable even at the filtration linear velocity of (LV) of 85 LMH but tended to increase at 100 LMH or more in Examples 2 and 3. 
     As described above, it was possible to significantly improve the amount of treated water per unit volume in Examples 1 and 2 above compared to Comparative Examples 1 and 2. 
     Next, the hollow-fiber membrane module according to a second embodiment of the invention will be described. 
       FIG. 13  is a perspective view of the hollow-fiber membrane module according to the embodiment of the invention,  FIG. 14  is a cross-sectional view of the VII-VII′ cross-section of  FIG. 13 , and  FIG. 15  is a cross-sectional view of the VIII-VIII′ cross-section of  FIG. 13 . 
     As illustrated in  FIG. 13  to  FIG. 15 , a hollow-fiber membrane module  51  includes a hollow-fiber membrane stacked body  53  formed by stacking a hollow-fiber membrane sheet and a water collecting member  55  for collecting the water filtered by the hollow-fiber membrane stacked body  53 . The hollow-fiber membrane stacked body  53  is liquid tightly fixed to a water-collecting member  55  using a fixing resin  57 . 
     The hollow-fiber membrane sheet is a hollow-fiber membrane sheet formed by arranging and binding a great number of hollow-fiber membranes in a sheet shape, and the hollow-fiber membrane stacked body  53  is constituted by stacking the plurality of hollow-fiber membrane sheets. Moreover, at least one end part of the hollow-fiber membrane constituting the hollow-fiber membrane sheet is cut in the direction perpendicular to the extending direction of the hollow-fiber membrane, and the end part of the hollow-fiber membrane is in an open state. 
     The material of the hollow-fiber membrane is not particularly limited, and examples thereof may include a polysulfone-based resin, polyacrylonitrile, a cellulose derivative, a polyolefin such as polyethylene or polypropylene, a fluorine-based resin such as polyvinylidene fluoride or polytetrafluoroethylene, a chlorine-based resin such as polyvinyl chloride or polyvinylidene chloride, a polyamide, a polyester, a polymethacrylate, and a polyacrylate. In addition, the material may be a copolymer of these resins or one obtained by introducing a substituent into a part thereof. Furthermore, the material may be one obtained by mixing two or more kinds of resins. Meanwhile, the pore size, porosity, thickness, outer diameter, or the like of the hollow-fiber membrane are not particularly limited as long as a hollow-fiber membrane is usable as a filtration membrane, but, for example, the outer diameter thereof is preferably in a range of from 20 to 4000 μm, the pore size thereof is preferably in a range of from 0.001 to 5 μm, the porosity thereof is preferably in a range of from 20 to 90%, and the thickness thereof is preferably in a range of from 5 to 300 μm. 
     The water collecting member  55  has a long shape extending along the width direction of the hollow-fiber membrane sheet constituting the hollow-fiber membrane stacked body  53 . In addition, a water intake port  59  for collecting the purified water is formed at the end face of the longitudinal direction of the water collecting member  55 . Moreover, the water collecting member  55  includes an opening part  61  leading to the inside, and one end of the hollow-fiber membrane stacked body  53  is inserted in this opening part  61 . Furthermore, the water collecting member  55 , in addition to the opening part  61  leading to the inside of the water collecting member  55 , is equipped with a pair of side walls  63  and  65  extending from the opening part  61  on both sides of the opening part  61  and a water collecting channel  67  which is formed between the side walls  63  and  65  and communicates with the opening of the end part of the hollow-fiber membrane. A reinforcing structure  69  which is constituted with a plurality of columnar bodies  69   a ,  69   b ,  69   c , . . . for coupling the pair of side walls  63  and  65  with each other is provided in the water collecting channel  67 . 
     The material for forming the water collecting member  55  may be any one exhibiting mechanical strength and durability, and it is possible to use, for example, a polycarbonate, a polysulfone, a polyolefin, polyvinyl chloride (PVC), an acrylic resin, an ABS resin, a modified polyphenylene ether (modified PPE), a polyester resin such as a PET resin and a PBT resin, or the like. A hydrocarbon-based resin such as a polyolefin which is completely combustible without emitting a toxic gas by combustion is preferable in a case in which incineration is required after use. 
     The reinforcing structure  69  couples the side walls  63  and  65  with each other in the water collecting channel  67  using the plurality of columnar bodies  69   a ,  69   b ,  69   c , . . . . The columnar bodies  69   a ,  69   b ,  69   c , . . . extend in the plane direction of the side walls  63  and  65 , that is, the width direction of the water collecting member  55 . Moreover, The plurality of columnar bodies  69   a ,  69   b ,  69   c , . . . are arranged along the extending direction of the water collecting member  55 . The plurality of columnar bodies  69   a ,  69   b ,  69   c , . . . are preferably provided at the position at which the displacement is greatest when a positive pressure or a negative pressure is applied to the water collecting member  55 , that is, the central part in the height direction of the water collecting channel  67 . Furthermore, the columnar bodies  69   a ,  69   b ,  69   c , . . . may be provided, for example, in the vicinity of the interface of the fixing resin  57  and the side walls  63  and  65  of the accumulation member since stress is easily applied to this position due to the structure of the water collecting member  55 . Each of the columnar bodies  69   a ,  69   b ,  69   c , . . . has a streamlined shape such as a circular cross-section or an elliptical cross-section in order to decrease the resistance force to the flow of filtered water in the water collecting channel. In addition, the cross-section of each of the columnar bodies may have an asymmetrical shape or an acute-angled shape having an acute angle toward the water intake port  59 . Moreover, the projected area of the plurality of the columnar bodies  69   a ,  69   b ,  69   c , . . . arranged along the extending direction of the water collecting channel  67  when viewed from the longitudinal direction of the water collecting member  55  is smaller as the columnar body is closer to the water intake port  59  and greater as the columnar body is farther from the water intake port. 
     Such a water collecting member  5  may be formed as an integrally molded article or by combining two components in order to secure the bonding strength of the side walls  63  and  65  and the columnar bodies  69   a    69   b ,  69   c, . . . .    
     In the case of forming a water collecting member by two components, a first component having at least one side wall and a columnar body extending therefrom and a second component having the other side wall are prepared, and then the bonding part between these first component and second component and the tip of the columnar body and the side wall of the second component are respectively bonded by, for example, heat welding, ultrasonic welding, vibration welding, laser welding, adhesion. 
     Hereinafter, the action of the hollow-fiber membrane module  51  will be described. 
     The hollow-fiber membrane module  51  is impregnated with water to be treated in the case of filtering the water to be treated by the hollow-fiber membrane module  51 . Thereafter, a pump is coupled to the water intake port  59  of the hollow-fiber membrane module  51  and actuated, and a negative pressure is applied to the inside of the water collecting channel  67  and the hollow-fiber membrane of the hollow-fiber membrane module  51 . This allows water to be treated surrounding the hollow-fiber membrane to be drawn into the hollow-fiber membrane and thus to be filtered by the hollow-fiber membrane. Thereafter, the filtered water passes through the hollow-fiber membrane to be collected in the water collecting channel  67  and then passes through the water intake port  59  to be discharged from the hollow-fiber membrane module  51 . A negative pressure is applied to the inside of the water collecting channel  67  and thus force to contract the water collecting member  55  is applied at the time of filtration treatment by the hollow-fiber membrane module  51 , but the side walls  63  and  65  of the water collecting member  55  are coupled with each other by the reinforcing structure  69  so as to be reinforced and thus the deformation of the side walls  63  and  65  can be relieved. 
     In addition, a washing liquid is introduced into the water collecting channel  67  and the hollow-fiber membrane via the water intake port  59  and also a positive pressure is applied to the inside of these in the case of washing the hollow-fiber membrane module  51 . This makes it possible to remove the contaminants adhered to the fine pores of the hollow-fiber membrane. A positive pressure is applied to the inside of the water collecting channel  67  and thus force to expand the water collecting member  55  is applied at the time of washing the hollow-fiber membrane module  51 , but the side walls  63  and  65  of the water collecting member  55  are coupled with each other by the reinforcing structure  69  so as to be reinforced and thus the deformation of the side walls  63  and  65  can be relieved. 
     As described above, according to the hollow-fiber membrane module  1  according to the embodiment of the invention, it is possible to improve the pressure resistant performance of the hollow-fiber membrane module  51  by a simple structure in which the columnar bodies  69   a ,  69   b ,  69   c , . . . are provided in the water collecting channel  67 . In addition, it is not required to mix a reinforcing agent with the water collecting member  55  or to use a special material as the water collecting member  55  when using the reinforcing structure  69  having the columnar bodies  69   a ,  69   b ,  69   c , . . . , and thus it is eliminated that the hollow-fiber membrane module  51  may not be used depending on the substance contained in the water to be treated. This makes it possible to improve the degree of freedom of the use application of the hollow-fiber membrane module  51 . 
     Hereinafter, Example and Comparative Example of the invention will be described in detail. 
     The comparative test was conducted without using the hollow-fiber membrane in Comparative Example and Example in order to evaluate the strength of the following case to the limit. 
     Example 3 
     Two cases having external dimensions of L340 mm×W6 mm×H50 mm and a divided structure were prepared, and these were superimposed and welded to fabricate an ABS water collecting member of L340 mm×W12 mm×H50 mm. An opening part of L300 mm×W6 mm×20 mm and a water collecting channel of L300 mm×W6 mm×H20 mm corresponding to the opening part were formed on the water collecting member. In addition, a water intake port having an inner diameter of φ6 mm was formed on both end parts of the water collecting member. Moreover, five columnar bodies having a circular cross-section with an outer diameter of φ6 mm were evenly formed at right and left and top and bottom of the water collecting channel. The water collecting member and the coupling structure were welded by a solvent adhesive (ESLON No. 73). The stacked body of hollow-fiber membrane sheet was fixed to the water collecting member using a polyurethane resin (4423/4426 Nippon Polyurethane) as the fixing resin of the hollow-fiber membrane. Thereafter, the water intake port was sealed, pressure was applied to the inside of the water collecting passage, and the applied pressure and the maximum displacement of the water collecting member was measured. In addition, the maximum pressure at which the water collecting member is fractured by the pressurization was measured. 
     Comparative Example 3 
     The same water collecting member for evaluation as that of Example except that the water collecting channel does not have a reinforcing structure was fabricated. Thereafter, the water intake port of the water collecting member was sealed, pressure was applied to the water collecting member, and the applied pressure and the maximum displacement of the case was measured. In addition, the maximum pressure at which the water collecting member is fractured by the pressurization was measured. 
     The measurement results in Example 3 and Comparative Example 3 above are presented in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Dimension of 
                 Dimension 
                 Deformation 
                   
               
               
                   
                 water 
                 of 
                 quantity of 
                 Pressure at 
               
               
                   
                 collecting 
                 columnar 
                 water collecting 
                 the time of 
               
               
                   
                 member 
                 body 
                 member 
                 fracture 
               
               
                   
                 (L × W × H) 
                 (mm) 
                 (mm/0.1 MPa) 
                 (MPa) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Example 
                 340 × 12 × 50 
                 φ6 mm × 
                 0.2 
                 0.50 
               
               
                   
                   
                 5 pieces 
               
               
                 Comparative 
                 340 × 12 × 50 
                 — 
                 0.8 
                 0.35 
               
               
                 Example 
               
               
                   
               
            
           
         
       
     
     As can be seen from the above, it is verified that the water collecting member of Example 3 in which a columnar body was formed on the water collecting channel exhibits a less deformation quantity and higher pressure resistance than the water collecting member of Comparative Example 3. 
       FIG. 16  is a perspective view illustrating a flat type hollow-fiber membrane module according to an embodiment of the invention. 
     First, as illustrated in  FIG. 16 , a flat type hollow-fiber membrane module  1  includes a stacked body  3  formed by bundling hollow-fiber membranes and a water collecting member  5  to which this hollow-fiber membrane stacked body  3  is fixed. 
     The hollow-fiber membrane stacked body  3  is constituted by stacking a plurality of hollow-fiber membrane sheets formed by arranging and binding a great number of hollow-fiber membranes in a sheet shape. This hollow-fiber membrane stacked body  3  is fixed to the water collecting member  5  using a fixing resin  7 . The number of sheets constituting the hollow-fiber membrane stacked body  3  is preferably from 1 to 15 sheets and even more preferably from 2 to 10 sheets. 
     The material of the hollow-fiber membrane constituting the hollow-fiber membrane stacked body  3  is not particularly limited, and examples thereof may include a polysulfone-based resin, polyacrylonitrile, a cellulose derivative, a polyolefin such as polyethylene or polypropylene, a fluorine-based resin such as polyvinylidene fluoride or polytetrafluoroethylene, a chlorine-based resin such as polyvinyl chloride or polyvinylidene chloride, a polyamide, a polyester, a polymethacrylate, and a polyacrylate. In addition, the material may be a copolymer of these resins or one obtained by introducing a substituent into a part thereof. Furthermore, the material may be one obtained by mixing two or more kinds of resins. Meanwhile, the pore size, porosity, thickness, outer diameter, or the like of the hollow-fiber membrane are not particularly limited as long as a hollow-fiber membrane is usable as a filtration membrane, but, for example, the outer diameter thereof is preferably in a range of from 20 to 4000 the pore size thereof is preferably in a range of from 0.001 to 5 μm, the porosity thereof is preferably in a range of from 20 to 90%, and the thickness thereof is preferably in a range of from 5 to 300 μm. 
     The arrangement direction of the hollow-fiber membrane is not particularly limited, but it is preferable that the hollow-fiber membrane is arranged roughly parallel to the flow direction of the liquid to be treated. In such a case, there is an effect of reducing the deposition or strain of the impurities onto the hollow-fiber membrane since there is no obstacle such as the hollow-fiber membrane which is perpendicular to the flow direction when the impurities to pass through between the great number of hollow-fiber membranes, for example, in the case of a highly contaminated liquid in which the liquid to be treated contains a great amount of impurities. 
     Furthermore, the arrangement direction of the hollow-fiber membrane is preferably that the lengthwise direction of the hollow-fiber membrane is the longitudinal direction, namely the up and down direction. In such a case, a synergistic effect with the effect of preventing the deposition of impurities described above is exhibited since, for example, it is possible to roughly parallelize the upward flow direction of the liquid to be treated that is generated at the time of air bubbling washing often used to wash the impurities and the extending direction of the hollow-fiber membrane. 
     It is possible to use an epoxy resin, an unsaturated polyester resin, a polyurethane resin, a silicone-based filler, various kinds of hot melt resins as the fixing resin  7  of the hollow-fiber membrane stacked body  3 , and the fixing resin  7  can be appropriately selected. In addition, the initial viscosity of the fixing resin is from 3,000 to 200,000 mPa·s, preferably from 5,000 to 100,000 mPa·s, and even more preferably from 10,000 to 50,000 mPa·s. The viscosity can be appropriately selected depending on the outer diameter of the hollow-fiber membrane and the number of sheets or the like constituting the hollow-fiber membrane stacked body. 
     The water collecting member  5  has an elongated shape extending along the width direction of the hollow-fiber membrane sheet constituting the hollow-fiber membrane stacked body  3 . In addition, a water collecting port  9  for collecting the purified water is formed on the end face in the longitudinal direction of the water collecting member  5 . 
       FIG. 17  is a cross-sectional view illustrating a cross-section of a water collecting member. This cross-sectional view illustrates a cross-section of the water collecting member in the direction perpendicular to the longitudinal direction (width direction of the water collecting member). 
     As illustrated in  FIG. 17 , the water collecting member  5  has an opening part  11  leading to the inside, and one end of the hollow-fiber membrane stacked body  3  is inserted in this opening part  11 . Furthermore, the water collecting member  5 , in addition to the opening part  11  leading to the inside of the water collecting member  5 , is equipped with a pair of side walls  13  and  15  extending from the opening part  11  on both sides of the opening part  11  and a water collecting passage  17  formed on the side opposite to the opening part  11  with respect to the side walls  13  and  15 . The water collecting member  5  is formed by bonding two members of a first member  19  and a second member  21 . Each of the first member  19  and the second member  21  has a shape obtained by dividing the water collecting member  5  in the longitudinal direction at one location in the width direction of the water collecting member  5 . The water collecting member  5  is integrally formed by bonding the bonding parts  23  and  25  which are formed on the first member  19  and the second member  21 , respectively and in a cylindrical shape, and the bonding surfaces (not illustrated in the drawing) formed on both sides in the longitudinal direction of the first member  19  and the second member  21  to each other. 
     As the method for bonding the first member  19  and the second member  21  of the water collecting member  5 , it is possible to use heat welding, ultrasonic welding, vibration welding, laser welding, adhesion or the like. In addition, it is possible to improve the reliability of airtightness at the bonding parts of the first member  19  and the second member  21 , for example, by sandwiching a seal member such as a rubber flat packing between the first member  19  and the second member  21 . Moreover, a method may be adopted in which the seal member sandwiched between the first member  19  and the second member  21  is fastened by a mechanical fastening means (for example, bolts and nuts). 
     The opening part  11  of the water collecting member  5  has a dimension enough to accommodate the hollow-fiber membrane stacked body  3 . In addition, the hollow-fiber membrane stacked body  3  is fixed in the region sandwiched by the side walls  13  and  15  on the water collecting passage  17  side of the opening part  11  by the fixing resin  7 . Moreover, a protruding part  27  for reinforcement is provided on the side walls  13  and  15 , and the protruding part  27  has a shape to bite into the fixing resin  7  portion. The opening of the end part of the hollow-fiber membrane is exposed on the water collecting passage  17  side of the hollow-fiber membrane stacked body  7 , and water purified by the hollow-fiber membrane flows into the water collecting passage  17 . 
     Here, the water collecting passage  17  refers to the space enclosed by the first member  19 , the second member  21 , the fixing resin  7 , and the hollow-fiber membrane stacked body  3  and receives the purified water filtered by the hollow-fiber membrane. The end part in the longitudinal direction of the water collecting passage  17  communicates with the water collecting port  9  of the water collecting member  5 . 
     In addition, it is possible to dispose the cylindrical-shaped bonding parts  23  and  25  extending in the width direction of the water collecting member  5  inside the water collecting passage  17  if necessary. These bonding parts  23  and  25  have the function of a reinforcing rib for suppressing the deformation of the side walls  13  and  15  by the positive pressure/negative pressure applied to the inside of the flat type hollow-fiber membrane module  1  and extend at right angles to the direction in which the water collecting passage  17  extends. Moreover, it is preferable that the bonding parts  23  and  25  have a cylindrical shape in terms that the bonding parts  23  and  25  reduce the pressure loss due to the water flow in the water collecting passage  17 . In addition, the bonding parts  23  and  25  may have a fitted shape as illustrated in  FIG. 20 . 
     The material of the first member  19  and the second member  21  constituting the water collecting member  5  may be one exhibiting mechanical strength and durability, and it is possible to use a polycarbonate, a polysulfone, a polyolefin, PVC (polyvinyl chloride), an acrylic resin, an ABS resin, a modified PPE (polyphenylene ether), a PET resin, a PBT resin or the like. A hydrocarbon-based resin such as a polyolefin which is completely combustible without emitting a toxic gas by combustion is preferable in a case in which incineration is required after use. 
     In such a flat type hollow-fiber membrane module  1 , the water purified by the hollow-fiber membrane flows into the water collecting passage  17  through the opening formed at the end of the hollow-fiber membrane, and further the water flowed into the water collecting passage  17  flows toward the downstream side from the water collecting port  9  by applying a negative pressure to the inside of the flat type hollow-fiber membrane module  1 . 
     Next, a method for manufacturing the flat type hollow-fiber membrane module  1  described above will be described in detail. 
       FIG. 18  is a plan view illustrating a hollow-fiber membrane sheet of a flat type hollow-fiber membrane module, and  FIG. 19  is a perspective view illustrating a manufacturing process of a flat type hollow-fiber membrane module. 
     The hollow-fiber membrane sheet  29  is constituted by arranging a great number of hollow-fiber membranes side by side and binding one ends of the hollow-fiber membranes to one another. It is possible to use tape, an adhesive, thermal fusion or the like as the method for binding the hollow-fiber membranes to one another. 
     In addition, in the method for manufacturing the flat type hollow-fiber membrane module  1 , first, a plurality of hollow-fiber membrane sheets  29  are prepared, and a fixing resin is coated in a region R of the vicinity of one side of the hollow-fiber membrane sheet  29   a  of the first sheet. The region R to be coated with a fixing resin is a region of the vicinity of either one of the end parts in the extending direction of the hollow-fiber membrane of the hollow-fiber membrane sheet  29 . 
     Next, a hollow-fiber membrane sheet  29   b  of the second sheet having the same dimensions as the hollow-fiber membrane sheet  29   a  of the first sheet is stacked on the hollow-fiber membrane sheet  29   a  of the first sheet so as to be exactly superimposed on the hollow-fiber membrane sheet  29   a  of the first sheet. The hollow-fiber membrane stacked body  3  is manufactured by performing these processes of coating a fixing resin and superimposing the hollow-fiber membrane sheet a predetermined number of times. 
     As a method for coating a fixing resin, it is desirable to coat while moving the nozzle head part of the ejection apparatus installed with a pump capable of constant ejection such as a gear pump, a positive load pump, and a mono pump at least in one axis (horizontal) direction at a constant speed from the viewpoint of performing quantitative coating. In addition, it is also possible to manually coat using a syringe (for example, SS-20ESZ manufactured by TERUMO CORPORATION), a brush, a spatula or the like. 
     As the coating shape of the fixing resin, it is desirable to coat in a film shape or at least one piece of bead shape. In addition, it is possible to adopt a method to spread the coated fixing resin with a spatula/brush or the like to be thin. 
     Next, the fixing resin is coated on one side surface of the ends on the side coated with the fixing resin of the hollow-fiber membrane stacked body  3  and/or the side wall  13  of the first member  19  of the water collecting member  5 . Thereafter, the end on the side coated with the fixing resin of the hollow-fiber membrane stacked body  3  is disposed on the side wall  13  of the first member  19  of the water collecting member  5 . At this time, the hollow-fiber membrane stacked body  3  is positioned at the position at which the end face of the end coated with the fixing resin of the hollow-fiber membrane stacked body  3  protrudes from the opening of the upper part of the water collecting passage  17  by from 0.5 to 15 mm. 
     Next, the fixing resin is coated on the other side surface of the ends on the side coated with the fixing resin of the hollow-fiber membrane stacked body  3  and/or the side wall  15  of the first member  21  of the water collecting member  5 . In addition, the bonding part  23  and the bonding surface  30  of the first member  19  and the bonding part  25  and the bonding surface  31  of the second member  21  are coated with a bonding adhesive. Thereafter, the second member  21  is bonded to the first member  19  and the hollow-fiber membrane stacked body  3  so as to be superimposed thereon. At this time, the bonding adhesive may be the same as the fixing resin or a different kind, and it can be appropriately selected depending on the purpose. 
     The hollow-fiber membrane sheets  29  are superimposed a predetermined number of times or more and adhered to one another as described above. Thereafter, the hollow-fiber membrane sheets  29  are sandwiched by the water collecting member  5  formed in a divided form, and this makes it possible to easily spread the fixing resin between the hollow-fiber membrane sheets  29 . In addition, it is possible to easily provide the protruding part  27  and the bonding parts  23  and  25  to the side wall when the first member  19  and the second member  21  are injection molded by forming the water collecting member  5  by the two members of the first member  19  and the second member  21 . Moreover, it is possible to improve the adhesive strength by the anchor effect since the protruding part  27  is allowed to bite into the fixing resin  7  of the hollow-fiber membrane stacked body  3  by providing this protruding part  27 . This makes it possible to firmly fix the hollow-fiber membrane stacked body  3  to the water collecting member  5  via the fixing resin  7 . Furthermore, it is possible to prevent the fixing resin  7  from dislocating from the water collecting member  5  when a negative pressure is applied to the inside of the water collecting member  5  and when the pressurized water or air flows into the flat type hollow-fiber membrane module  1  at the time of washing the hollow-fiber membrane and thus a positive pressure is applied to the inside of the water collecting member  5  by fixing the hollow-fiber membrane stacked body  3  to the water collecting member  5  by the protruding part  27 . In addition, it is possible to prevent the fixing resin  7  from dislocating from the water collecting member  5  and the water collecting members  19  and  21  from dislocating from each other 5 when a negative pressure is applied to the inside of the water collecting member  5  and when the pressurized water or air flows into the flat type hollow-fiber membrane module  1  at the time of washing the hollow-fiber membrane and thus a positive pressure is applied to the inside of the water collecting member  5  by providing the bonding parts  23  and  25 . 
     Meanwhile, the hollow-fiber membrane stacked body  3  is formed by a plurality of hollow-fiber membrane sheets  29   a  in the embodiment described above, but it is also possible to sandwich one sheet of the hollow-fiber membrane sheet between the first member and the second member. 
     Next, a modified example of the method for manufacturing a flat type hollow-fiber membrane module will be described. 
     In the manufacturing method of the flat hollow-fiber membrane module  1  according to the modified example, first, a fixing resin is coated on the side wall  13  of the first member  19  of the water collecting member  5 , and the hollow-fiber membrane sheet  29   a  of the first sheet is placed such that the region R of the vicinity of one side thereof is superimposed on the portion coated with the fixing resin described above. Subsequently, the region R of the vicinity of one side of the hollow-fiber membrane sheet  29   a  of the first sheet is coated with the fixing resin. 
     Next, the hollow-fiber membrane sheet  29   b  of the second sheet having the same dimensions as the hollow-fiber membrane sheet  29   a  of the first sheet is stacked on the hollow-fiber membrane sheet  29   a  of the first sheet so as to be exactly superimposed on the hollow-fiber membrane sheet  29   a  of the first sheet. Thereafter, the process of coating a fixing resin and the process of superimposing a hollow-fiber membrane sheet are repeated a predetermined number of times. 
     Next, the fixing resin is coated on the region R of the vicinity of one side of the hollow-fiber membrane stacked body  3 , and the bonding part  23  and the bonding surface  30  of the first member  19  and/or the bonding part  25  and the bonding surface  31  of the second member  21  are coated with a bonding adhesive. Thereafter, the second member  21  is bonded to the first member  19  and the hollow-fiber membrane stacked body  3  so as to be superimposed thereon. At this time, the bonding adhesive may be the same as the fixing resin or a different kind, and can be appropriately selected depending on the purpose. 
     It is possible to obtain the same effect as that of the method for manufacturing a flat type hollow-fiber membrane module described above even according to such a modified example. 
     In addition, using such a manufacturing method makes it possible to perform the work to fix the water collecting member at both ends of the hollow-fiber membrane at the same time in the state in which the hollow-fiber membrane is horizontally arranged, for example, in the case of providing the water collecting member at both ends of the hollow-fiber membrane. Moreover, in the manufacturing method described above, the fixing resin is directly coated on the hollow-fiber membrane sheet, and thus it is not required to consider the time until the fixing resin spreads through between the hollow-fiber membranes and it is possible to use a fixing resin having a relatively high viscosity and a fast cure rate. In other words, in the manufacturing method used in the related art, it is required to use a fixing resin having a slow cure rate so as not to be cured until the fixing resin spreads through between the hollow-fiber membranes, but in the manufacturing method according to the embodiment of the invention, it is possible to use a fixing resin having a relatively fast cure rate since it is not required to consider the time until the fixing resin spreads through between the hollow-fiber membranes. Furthermore, in the manufacturing method described above, it is not required a process of cutting the end part of the hollow-fiber membrane stacked body. This makes it possible to significantly shorten the time required for manufacturing a flat type hollow-fiber membrane module. 
     In addition, it is possible to decrease the gap between the hollow-fiber membrane sheets since it is not required to provide a gap to spread the fixing resin between the hollow-fiber membranes by adopting the process of sequentially stacking the hollow-fiber membrane sheets. This makes it possible to increase the packing density of the hollow-fiber membranes in the flat type hollow-fiber membrane module. 
     Bonding by an adhesive is mentioned in the present embodiment, but bonding by welding is also adoptable. 
     In addition, it is possible to easily provide the reinforcing structure, namely the protruding part and the reinforcing rib to the water collecting member at the time of injection molding when the water collecting member is constituted by two members. 
     EXPLANATIONS OF LETTERS OR NUMERALS 
     
         
           1  hollow-fiber membrane module 
           3  hollow-fiber membrane stacked body 
           5  water collecting member 
           7  fixing resin 
           17  water collecting passage 
           19  first member 
           21  second member 
           29  hollow-fiber membrane sheet 
           51  hollow-fiber membrane module 
           53  hollow-fiber membrane stacked body 
           55  water collecting member 
           57  fixing resin 
           59  water intake port 
           63  and  65  side wall 
           67  water collecting channel 
           69  reinforcing structure 
           69   a ,  69   b , and  69   c  columnar body 
           101  hollow-fiber membrane unit 
           103  hollow-fiber membrane module 
           107  air diffuser 
           111  hollow-fiber membrane sheet 
           113  hollow-fiber membrane sheet stacked body 
           115  case 
           115   a  thick wall part 
           115   b  reinforcing structure 
           117  water intake port 
           119  opening for fixation 
           121  fixing resin (potting resin) 
           125  water collecting path 
           127  convex part 
           129  collective water intake pipe 
           131  inflow opening 
           135  water intake pipe