Abstract:
A wastewater treatment apparatus that obtains treated water by adding a flocculant and magnetic powder to wastewater accumulated in a tank to thereby generate flocculated magnetic flocs, and recovering the magnetic flocs by means of a magnetic force to thereby remove the magnetic flocs from the wastewater, comprising: 
     a magnetic flocs treatment device which treats the recovered magnetic flocs and which comprises a high pressure pump and a magnetic separation portion; 
     wherein the magnetic separation portion has a structure in which fluid piping is arranged at a magnetic field generating portion, and magnetic powder in the magnetic flocs is recovered by using the high pressure pump to pump the recovered magnetic flocs to the fluid piping of the magnetic separation portion, and causing the magnetic powder in the magnetic flocs to attach to the fluid piping by means of a magnetic force of the magnetic field generating portion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a wastewater treatment apparatus, and more particularly to a wastewater treatment apparatus that treats wastewater by flocculation and magnetic separation by adding a flocculant and magnetic powder to the wastewater. 
         [0003]    2. Description of the Related Art 
         [0004]    A water treatment method that uses a flocculation and magnetic separation system obtains treated water by adding a flocculant and magnetic powder to wastewater that is the object of treatment, generating flocculated flocs (hereunder, referred to as “magnetic flocs”) by agitating the resulting mixture, and recovering the magnetic flocs using a magnetic force produced by a magnetic separation apparatus. 
         [0005]    According to this method, magnetic flocs that include magnetic powder are recovered, and it is necessary to dispose of the recovered magnetic flocs as industrial waste. Consequently, the cost of supplying magnetic powder and the cost of disposing of the recovered flocs as industrial waste lead to an increase in running costs. 
         [0006]    Technology for solving the foregoing problem is known, as disclosed in Japanese Patent Application Laid-Open No. 11-123399 and Japanese Patent Application Laid-Open No. 11-207399, in which sludge containing magnetic powder is decomposed by a hydrothermal reaction and the volume of sludge is reduced. 
         [0007]    According to the wastewater treatment apparatuses disclosed in Japanese Patent Application Laid-Open Nos. 11-123399 and 11-207399, sewage is purified by flocculation and magnetic separation using a magnetic separation apparatus, sludge that is generated at that time is hydrothermally treated at a high temperature and a high pressure, and magnetic powder is recovered by magnetic separation in a high-temperature and high-pressure line. 
         [0008]    However, according to the wastewater treatment apparatuses disclosed in Japanese Patent Application Laid-Open Nos. 11-123399 and 11-207399, there has been the problem that in order to obtain sufficient floc decomposition performance when subjecting sludge to hydrothermal treatment at a high temperature and a high pressure, not only is a significant amount of energy required, but the structure of the hydrothermal apparatus used for the floc decomposition process also becomes complex. In this connection, according to Japanese Patent Application Laid-Open No. 11-123399, sludge is pressurized to 10 MPa or more and heated to less than 350° C., and thereafter is lead to a magnetic powder separator. According to Japanese Patent Application Laid-Open No. 11-207399, sludge is pressurized to approximately 2 MPa and heated to around 200° C., and thereafter is lead to a magnetic powder separator. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention has been made in consideration of the foregoing circumstances, and an object of the invention is to provide a wastewater treatment apparatus that can decrease the amount of energy required for decomposing recovered magnetic flocs, and can also recover magnetic powder from recovered magnetic flocs with high efficiency with a simple apparatus configuration. 
         [0010]    To achieve the above object, the present invention provides a wastewater treatment apparatus that obtains treated water by adding a flocculant and magnetic powder to wastewater accumulated in a tank to thereby generate flocculated magnetic flocs, and recovering the magnetic flocs by means of a magnetic force to thereby remove the magnetic flocs from the wastewater, the wastewater treatment apparatus including a magnetic flocs treatment device which treats the recovered magnetic flocs and which has a high pressure pump and a magnetic separation portion; wherein the magnetic separation portion has a structure in which fluid piping is arranged at a magnetic field generating portion, and magnetic powder in the magnetic flocs is recovered by using the high pressure pump to pump the recovered magnetic flocs to the fluid piping of the magnetic separation portion, and causing the magnetic powder in the magnetic flocs to attach to the fluid piping by means of a magnetic force of the magnetic field generating portion. 
         [0011]    According to the present invention, water including recovered magnetic flocs is pressurized to a predetermined pressure by a high pressure pump, and the water is pumped to fluid piping of a magnetic separation portion. A shear force is applied to the magnetic flocs by the pumping action, and as a result of the shear force the magnetic flocs are converted into water in which the magnetic powder and suspended solid matter that had been flocculated up to that time are separated into individual pieces. Subsequently, when the water passes through the fluid piping, the separated magnetic powder is caused to attach to the fluid piping by a magnetic force of the magnetic field generating portion and recovered. Thus, according to the present invention, it is possible to decrease the amount of energy required to decompose recovered magnetic flocs, and magnetic powder can be recovered at a high efficiency from recovered magnetic flocs using a simple apparatus configuration that comprises a high pressure pump and a magnetic separation portion. 
         [0012]    Preferably, the present invention includes a conduit that returns magnetic powder recovered with the fluid piping to the tank. 
         [0013]    According to the present invention, since recovered magnetic powder can be reused, a wastewater treatment apparatus can be provided that reduces waste matter and running costs. 
         [0014]    Preferably, in the present invention, the magnetic field generating portion includes a magnetic drum that has a plurality of electromagnets or permanent magnets mounted in a vicinity of a surface of the magnetic drum, and a cylindrical pipe made of metal that surrounds the drum, wherein the fluid piping is wound around the circumference of the cylindrical pipe. 
         [0015]    According to the present invention, since the length of the fluid piping can be made sufficiently long by winding the fluid piping around the magnetic drum, the magnetic powder can undergo adequate magnetic separation. Further, although a problem of pressure loss in fluid piping may occur when the fluid piping has a small diameter and a long length, since the present structure uses a pump that originally has a sufficiently high pressure, the aforementioned problem of a pressure loss does not arise. 
         [0016]    In the present invention, preferably the magnetic drum is capable of a reciprocating action within the cylindrical pipe, a plurality of systems of the fluid piping are provided at one magnetic field generating portion to which the magnetic drum moves, and the wastewater treatment apparatus has a switching valve that causes magnetic flocs to flow into the plurality of systems of fluid piping. 
         [0017]    According to the present invention, a flow channel is switched by means of a switching valve to cause magnetic flocs to flow to one fluid piping system among a plurality of systems of fluid piping. At this time, the magnetic drum is moved inside the cylindrical pipe so as to be positioned at one magnetic field generating portion that corresponds to the one fluid piping system, and another fluid piping system is cleaned. Subsequently, when cleaning of the other fluid piping system ends, the flow channel is switched by the switching valve to cause magnetic flocs to flow to the other fluid piping system. At this time, the magnetic drum is moved inside the cylindrical pipe so as to be positioned at another magnetic field generating portion that corresponds to the other fluid piping system, and the one fluid piping system is cleaned. It is thus possible to continuously operate the wastewater treatment apparatus. Further, since a magnetic force generated by the magnetic drum is not acting on a fluid piping system when the fluid piping in question is being cleaned, magnetic powder that has attached to the fluid piping can be easily detached by the cleaning water. The detached magnetic powder is returned to a tank through a conduit together with the cleaning water and reused. 
         [0018]    In the present invention, preferably, in the fluid piping, a magnetic flocs supply channel and a cleaning water supply channel are linked through a switching valve, and the switching valve is positioned on an upstream side of a pressure reducing device that is disposed between the high pressure pump and the fluid piping. 
         [0019]    According to the present invention, by disposing a pressure reducing device at a stage subsequent to the high pressure pump, a shear force applied to the magnetic flocs can be applied to the magnetic flocs at a stage prior to the fluid piping. By providing a pressure reducing device, recovery of magnetic powder is performed with even greater efficiency. By arranging a switching valve that switches between a magnetic flocs supply channel and a cleaning water supply channel on the upstream side of the pressure reducing device, it is possible to clean the pressure reducing device with the cleaning water. As a result, the durability of the pressure reducing device is enhanced and the performance of the pressure reducing device can be maintained. 
         [0020]    In the present invention, preferably the magnetic flocs treatment device includes a pH adjustment device, and after the magnetic flocs are adjusted to a pH between 8 and 14 by the pH adjustment device, the magnetic flocs are pumped by the high pressure pump, and magnetic powder is recovered by the magnetic separation portion. 
         [0021]    According to the present invention, by making the pH of magnetic flocs between 8 and 14 by means of a pH adjustment device that is disposed at a stage prior to the high pressure pump, it is possible to increase the efficiency of decomposing the magnetic flocs by a magnetic flocs treatment device that is provided at a subsequent stage. 
         [0022]    In the present invention, preferably the magnetic flocs treatment device includes a heating device, and after the magnetic flocs are heated to a temperature between 40 and 100° C. by the heating device, the magnetic flocs are pumped by the high pressure pump, and magnetic powder is recovered by the magnetic separation portion. 
         [0023]    According to the present invention, by heating magnetic flocs to a temperature between 40 and 100° C. by means of a heating device that is disposed at a stage prior to the high pressure pump, it is possible to increase the efficiency of decomposing the magnetic flocs by a magnetic flocs treatment device that is provided at a subsequent stage. 
         [0024]    In the present invention, preferably the magnetic flocs treatment device includes an electrolysis device, and after the magnetic flocs are subjected to an electrolysis reaction by the electrolysis device, the magnetic flocs are pumped by the high pressure pump, and magnetic powder is recovered by the magnetic separation portion. 
         [0025]    According to the present invention, when magnetic flocs are electrolyzed by an electrolysis device disposed at a stage prior to the high pressure pump, in a case in which water to be treated includes salt content such as NaCl, the pH is shifted to the alkali side by the electrolysis, and energy generated by the electrolysis is ultimately imparted to the flocs in the form of heat, so that the temperature also increases. More specifically, since alkalization and an increased temperature can be achieved just by electrolysis, floc decomposition by the magnetic flocs treatment device at a subsequent stage is facilitated. 
         [0026]    According to the present invention, it is possible to decrease the amount of energy required to decompose recovered magnetic flocs and recover magnetic powder at a high efficiency from recovered magnetic flocs with a simple apparatus configuration. Further, according to the present invention, since recovered magnetic powder can be reused, a wastewater treatment apparatus can be provided that reduces waste matter and running costs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a structural drawing that illustrates a wastewater treatment apparatus according to a first embodiment of the present invention; 
           [0028]      FIG. 2  is an explanatory drawing that illustrates an example of the configuration of a pressure reducing device; 
           [0029]      FIG. 3  is a structural drawing that illustrates a wastewater treatment apparatus according to a second embodiment of the present invention; 
           [0030]      FIG. 4  is a structural drawing that illustrates a wastewater treatment apparatus according to a third embodiment of the present invention; 
           [0031]      FIG. 5  is an explanatory drawing that illustrates a structure of a magnetic powder recovery and magnetic separation portion; 
           [0032]      FIG. 6  is an explanatory drawing that illustrates another structure of a magnetic powder recovery and magnetic separation portion; and 
           [0033]      FIG. 7  is a structural drawing that illustrates a wastewater treatment apparatus according to a fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    Preferred embodiments of the wastewater treatment apparatus according to the present invention are described hereunder in accordance with the attached drawings. 
         [0035]      FIG. 1  is a structural drawing that illustrates a wastewater treatment apparatus according to a first embodiment of the present invention. 
         [0036]    Wastewater (wastewater that includes small pieces of suspended matter or emulsified oil particles) that is water to be treated is pumped from a raw water tank  1  by a raw water pump  2  to a rapid agitation tank  6  of the wastewater treatment apparatus. At this time, the wastewater is accumulated in the rapid agitation tank  6 . An inorganic flocculant such as, for example, PAC (polyaluminum chloride), ferric sulfate, or aluminum sulfate is added to the rapid agitation tank  6  from an inorganic flocculant tank  3  using an inorganic flocculant injection pump (not shown), and the resulting mixture is rapidly agitated. At this time, a large number of small lumps referred to as “microflocs” are formed by the effect of the flocculant as the collision frequency of the suspended matter and oil particles is increased by the rapid agitation. While the mixture is inside the rapid agitation tank  6 , or when the mixtures leaves the rapid agitation tank  6 , magnetic powder such as magnetite is added thereto from the magnetic powder tank  4  by a magnetic powder injection pump (not shown). 
         [0037]    After the water to be treated that includes microflocs has left the rapid agitation tank  6 , the water to be treated flows into a slow agitation tank  7 . At this time, polymeric flocculants are added thereto from a polymeric flocculant tank  5  by means of a polymeric flocculant pump (not shown). By slowly agitating the resulting mixture in the slow agitation tank  7 , flocculated magnetic flocs develop. In this case, an anionic polymer is desirable as the polymeric flocculant. For example, polyacrylamide is suitable as the polymeric flocculant. When polyacrylamide is used, a structure may be considered in which the polyacrylamide is stored as powder and added to the polymeric flocculant tank  5  in fixed quantities with a feeder and agitated. Although an example is described above which uses an inorganic flocculant and an anionic polymeric flocculant, an effect similar to the effect described hereunder is also obtained in the case of using only a cationic polymeric flocculant without using an inorganic flocculant. 
         [0038]    The magnetic flocs generated as described above are conveyed with the water to a magnetic separation portion  8 . 
         [0039]    A magnetic drum  13  that contains therein a permanent magnet such as a neodymium magnet is arranged in the magnetic separation portion  8 . When flocculated water that contains the magnetic flocs passes the vicinity of the magnetic drum  13 , magnetic powder contained in the magnetic flocs is attracted by the magnetic force of the permanent magnet and attaches to the surface of the magnetic drum  13 . The magnetic flocs that attach to the surface of the magnetic drum  13  are lifted from the water to the air accompanying rotation of the magnetic drum  13 , and are scraped off by a scraper  14  and recovered. The magnetic flocs that are recovered (hereunder, referred to as “recovered flocs”) are fed to a recovered flocs decomposing apparatus (magnetic flocs treatment device)  15 . Further, the water from which magnetic flocs have been removed is discharged to outside from the magnetic separation portion  8  as treated water  10 . 
         [0040]    The recovered flocs are temporarily accumulated in a recovered flocs tank  9 . An agitator is provided in the recovered flocs tank  9 . Precipitation of the recovered flocs is prevented by agitating the contents inside the tank  9  using the agitator. 
         [0041]    Water including the recovered flocs of the recovered flocs tank  9  is pressurized to between 0.2 to 5 MPa approximately by a high pressure pump  12  such as a plunger type pump or a diaphragm type pump. Thereafter, the water is depressurized by a pressure reducing device  37  with a flow channel that has a narrow portion. When the recovered flocs pass through the pressure reducing device  37 , the flow rate quickens at the narrow portion of the flow channel of the pressure reducing device  37 , and the recovered flocs are decomposed by an increase in the shear stress. In this connection, the pressure reducing device  37  is not essential, and since a shear force can also be applied to the recovered flocs by directly pumping water that has been pressurized by the high pressure pump  12  to fluid piping  42  that is described later, magnetic powder  64  can be separated from the recovered flocs and the separated magnetic powder  64  can be recovered with the fluid piping  42 . 
         [0042]    An example of the pressure reducing device  37  is shown in  FIG. 2 . This is an example in which an orifice  70  is provided in piping  63  that links the high pressure pump  12  and the pressure reducing device  37  shown in  FIG. 1 . 
         [0043]    According to this pressure reducing device  37 , when a water current  68  of water including a large number of recovered flocs  67  is passing through the orifice  70 , the flow rate quickens when the water current  68  passes through a narrow opening  71  in the flow channel. The recovered flocs  67  are decomposed by an increase in the shear stress caused by the increased flow rate. As a result, a water current  69  is formed in which magnetic powder  64  and suspended solid matter  65  and the like that had been flocculated up to this time are separated into individual pieces. Accordingly, by providing a device that has a magnetic separation function at the stage subsequent thereto, it is possible to recover the magnetic powder (magnetic particles)  64  from the recovered flocs  67 . 
         [0044]    As well as the orifice  70 , a nozzle, or a back-pressure valve for which the pressure can be controlled or the like may be considered as the pressure reducing device  37 . In this case, the apparatus can be provided with excellent durability properties by using a diamond or ceramic material as the material of the portion at which the flow channel narrows. Further, if the portion at which the flow channel narrows is made in the shape of an orifice with a plurality of holes, the operations will not be obstructed even if one hole is blocked. The pressure reducing device  37  may also be a combination of an orifice that has a portion at which the flow channel narrows and a back-pressure valve for which the pressure can be controlled. In this case, exact pressure control can be performed in a state in which the durability of the back-pressure valve is ensured. 
         [0045]    However, once flocs have been decomposed the flocs will coagulate again if the flocs are left as they are. It is therefore necessary to recover only the magnetic powder  64  from flocs that are decomposed (hereunder, referred to as “decomposed flocs”) immediately after the pressure reducing device  37 . 
         [0046]    Consequently, according to the first embodiment, as shown in  FIG. 1 , the magnetic powder  64  is recovered by a magnetic powder recovery and magnetic separation portion (magnetic separation portion)  40 . The magnetic powder recovery and magnetic separation portion  40  is provided with a cylindrical electromagnet (magnetic field generating portion)  41 , and fluid piping  42  which is arranged around the circumference of the electromagnet  41  and through which decomposed flocs flows. 
         [0047]    By employing this structure, the flow of decomposed flocs that flows through the fluid piping  42  can be placed in a state with a greater turbulence than the slow agitation tank  7  by decreasing the diameter of the fluid piping  42  to some extent. It is thereby possible to implement magnetic separation in a state in which decomposed flocs do not redevelop into flocculated flocs. The high pressure pump  12 , the pressure reducing device  37 , and the magnetic powder recovery and magnetic separation portion  40  are included in the recovered flocs decomposing apparatus  15 . As described in the foregoing, the pressure reducing device  37  is not essential. 
         [0048]    While the decomposed flocs flow through the fluid piping  42 , only the magnetic powder  64  is attracted by the electromagnet  41  and builds up on a wall surface of the fluid piping  42  close to the electromagnet  41 . The other substances are discharged to a sludge tank  49  outside the magnetic powder recovery and magnetic separation portion  40  together with the flow of water. In this case, if the flow rate in the fluid piping  42  is fast, there is the possibility that the magnetic powder  64  that has built up will be detached and flow through the fluid piping  42  again. 
         [0049]    Therefore, according to the present structure, since the length of the fluid piping  42  is made sufficiently long by winding the fluid piping  42  around the electromagnet  41 , it is possible to adequately perform magnetic separation of the magnetic powder  64  using the optimal design. Further, although in some cases a problem of a pressure loss in the fluid piping  42  may arise when the diameter of the fluid piping  42  is reduced and the length thereof is lengthened, since the present structure is one that uses the high pressure pump  12  that originally has sufficient pressure, the above described problem regarding a pressure loss does not arise. 
         [0050]    After a certain amount of time elapses, valves  51  and  53  shown in  FIG. 1  are closed and valves  52  and  54  are opened, thereby allowing cleaning water to flow through the fluid piping  42  from the water tank  56  using a cleaning water pump  55 . At the same time, the passage of an electric current to the electromagnet  41  is stopped to break the magnetic field of the electromagnet  41 . As a result, the fluid piping  42  can be cleaned and reused, and at the same time the magnetic powder  64  can be recovered and returned to the magnetic powder tank  4  through the conduit  28 . 
         [0051]    In this case, by positioning the valve (switching valve)  52  into which the cleaning water flows on the upstream side of the pressure reducing device  37 , the inside of the pressure reducing device  37  can also be cleaned at regular intervals. Hence, the durability of the pressure reducing device  37  can be enhanced, and the pressure reducing capacity thereof can be maintained. Some of the treated water  10  may also be used as the water of the water tank  56 . 
         [0052]    The recovered flocs tank  9  is provided with, for example, a pH adjustment device  39  that has a pH meter, a tank for alkali such as NaOH, and an injection pump therefor. The efficiency with which the recovered flocs decomposing apparatus  15  decomposes recovered flocs at a subsequent stage can be increased by making the pH of the recovered flocs between 8 and 14. This is because flocculants exist for which a flocculation effect is normally highest in the vicinity of pH=7, which is neutral, and the flocculation effect deteriorates when the ph region is shifted away from a region with a high flocculation effect. 
         [0053]    Similarly, although flocs inside the recovered flocs tank  9  may be used as they are, it is preferable to heat the recovered flocs to a temperature between 40 and 100° C. using a heater  38  because the efficiency with which the recovered flocs decomposing apparatus  15  decomposes recovered flocs at a subsequent stage can be increased. At this time, if the region from the recovered flocs tank  9  to the pressure reducing device  37  is thermally insulated using a thermal insulating material, only a small amount of energy will be required for heating. 
         [0054]    It is also possible to improve the decomposition efficiency by employing a combination of both heating to a high temperature and alkalization as described above. Furthermore, it is possible to improve the decomposition efficiency by also increasing the temperature by heating with a heater or the like downstream of the high pressure pump  12 . 
         [0055]      FIG. 3  is a structural drawing that illustrates a wastewater treatment apparatus according to a second embodiment of the present invention. 
         [0056]    In the second embodiment, two of the magnetic powder recovery and magnetic separation portions  40  of the first embodiment illustrated in  FIG. 1  are provided in parallel to each other. According to this structure, continuous operation is enabled by causing the magnetic powder recovery and magnetic separation portions  40  perform a magnetic separation operation and a cleaning operation alternately. Naturally, a similar advantage can be obtained when three or more of the magnetic powder recovery and magnetic separation portions  40  are provided. In this connection, members of the second embodiment that are identical or similar to members of the first embodiment are designated by the same reference numerals, and a description of those members is omitted herein. 
         [0057]      FIG. 4  is a structural drawing that illustrates a wastewater treatment apparatus according to a third embodiment of the present invention. 
         [0058]    A difference between the third embodiment and the first and second embodiments shown in  FIG. 1  and  FIG. 3  is that permanent magnets are utilized in the magnetic powder recovery and magnetic separation portion  40 . In this connection, members of the third embodiment that are identical or similar to members of the first embodiment are designated by the same reference numerals, and a description of those members is omitted herein. 
         [0059]      FIG. 5  shows the structure of the magnetic powder recovery and magnetic separation portion  40  that utilizes permanent magnets. A cylindrical magnetic drum  43  has a structure in which a large number of permanent magnets  48  are mounted in the vicinity of the surface thereof. If the array of magnets is arranged in advance so that the magnetic poles of adjacent magnets are heteropolar, since a large magnetic gradient arises only in the vicinity of the magnetic drum  43 , a large magnetic force can be obtained and the magnetic field does not adversely affect other apparatuses that are arranged at positions away from the magnetic drum  43 . This structure is thus suitable for recovering and separating magnetic powder. 
         [0060]    The magnetic drum  43  is housed in a slidable state inside a metal cylinder  44 , and is driven by a driving apparatus  50  to perform a reciprocating action inside the cylinder  44 . Fluid piping  42   a  and  42   b  are wound around the outside of the cylinder  44  in a double helix configuration. 
         [0061]    For example, when the magnetic drum  43  is located at a position designated by reference numeral  21  inside the cylinder  44 , decomposed flocs flow through the fluid piping  42   a  from an inflow port  46   a  towards an outflow port  47   a.  In contrast, when the magnetic drum  43  moves to a position designated by reference numeral  22 , a switching valve of the fluid piping is switched and decomposed flocs flow through the fluid piping  42   b  from an inflow port  46   b  towards an outflow port  47   b.  At the same time, cleaning water flows through the fluid piping  42   a  from the inflow port  46   a  towards the outflow port  47   a.  According to this structure, it is possible to continuously and efficiently perform magnetic separation operations to recover magnetic powder without leaking magnetic powder. In this connection, although two systems of fluid piping, i.e.  42   a  and  42   b,  are described in this example, the number thereof is not limited to two, and three or more systems of fluid piping may be provided. In such case, the number of movement positions of the magnetic drum  43  inside the cylinder  44  will be three or more. 
         [0062]      FIG. 6  shows another structural example of the magnetic powder recovery and magnetic separation portion  40  that utilizes permanent magnets. 
         [0063]    Although the structure of the magnetic drum  43  shown in  FIG. 6  is the same as that of the embodiment shown in  FIG. 5 , the arrangement of the fluid piping  42   a  and  42   b  is different to the embodiment shown in  FIG. 5 . According to the structure shown in  FIG. 6 , for example, when the magnetic drum  43  is at a position designated by reference numeral  21  inside the cylinder  44 , decomposed flocs flow through the fluid piping  42   a  from the inflow port  46   a  towards the outflow port  47   a.  In contrast, when the magnetic drum  43  moves to a position designated by reference numeral  22 , a switching valve of the fluid piping is switched and decomposed flocs flow through the fluid piping  42   b  from an inflow port  46   b  towards an outflow port  47   b.  At the same time, cleaning water flows through the fluid piping  42   a  from the inflow port  46   a  towards the outflow port  47   a . According to the present structure, it is possible to continuously and efficiently perform magnetic separation operations to recover magnetic powder without leaking magnetic powder. In this case, by providing a small clearance between the regions designated by reference numerals  21  and  22 , it is possible to lessen the influence of the magnetic field of the adjacent region during the cleaning process. 
         [0064]      FIG. 7  is a structural drawing that illustrates a wastewater treatment apparatus according to a fourth embodiment. 
         [0065]    Although the fourth embodiment illustrates an example using the magnetic powder recovery and magnetic separation portion that uses permanent magnets as illustrated in  FIG. 3 , the same advantages are obtained as in the case of using an electromagnet as illustrated in  FIG. 1 . In this connection, members of the fourth embodiment that are identical or similar to members of the first embodiment are designated by the same reference numerals, and a description of those members is omitted herein. 
         [0066]    According to the fourth embodiment, an electrolysis device  58  is provided in the recovered flocs tank  9  instead of the pH adjustment device and heating device that are used in the example illustrated in  FIG. 1  and  FIG. 2 . 
         [0067]    When flocs in the recovered flocs tank  9  are electrolyzed by the electrolysis device  58 , if the water to be treated includes salt content such as NaCl the pH is shifted to the alkali side by the electrolysis, and energy produced by the electrolysis is ultimately applied to the flocs in the form of heat, so that the temperature also increases. More specifically, alkalization and a temperature increase can be achieved just by electrolysis, and this has the advantage of facilitating decomposition of recovered flocs by the recovered flocs decomposing apparatus  15  at a subsequent stage.