Abstract:
In a filtering and purifying system, bacteria in raw water are sterilized efficiently with ultraviolet rays, chemicals and the like at a pretreating step. The number of microorganisms such as bacteria remaining in the treated water is reduced remarkably, and the residue of plankton and organic substances as nutrients for bacteria in treated water is reduced by a coagulating and filtering treatment. It is thus possible to solve a problem that the treated water is deteriorated with time due to propagation of the bacteria.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a filtering/separating and purifying system for purification of water and for solid-liquid separation, and particularly, to the construction of the filtering and purifying system capable of reducing the number of microorganisms such as bacteria remaining in treated water.  
         [0002]     There is a magnetically separating and purifying system in which a fine metal net or a net knitted of polymer fibers is used as a through-flow separating membrane for the purpose of solid-liquid separation, and a flocculating agent and a magnetic powder are added to raw water containing polluting particles to be separated to thereby produce magnetic flocs. The magnetic flocs are then separated by the membrane, the magnetic flocs collected by the membrane are magnetically separated off and removed using a magnetic field-generating means, and a high-concentration sludge is recovered.  
         [0003]     This construction is described, for example, in JP-A-2002-273261. The filtering/separating and purifying system includes a membrane separating section comprising a net formed of fine stainless steel wires or polyester fibers and having openings of an opening size of, for example, several tens micrometers. To separate a fine polluting material smaller than a projected area and a projected diameter of the openings, for example, alumina sulfate, aluminum polychloride or iron polysulfate as a flocculating agent and a magnetic powder are previously added to raw water and stirred, and a fine solid suspended matter, algae and microorganisms in the raw water are coagulated into a size on the order of several hundred micrometers by the flocculating agent to form magnetic flocs. The magnetic flocs can not pass through the openings having the opening size of several tens micrometers, and are separated and caught with a high removal rate. The water penetrated through the membrane is purified water having a high quality with the residue of the fine solid suspended matter, algae and microorganisms in the raw water being several percents.  
         [0004]     The magnetic flocs caught on the membrane are washed away from the membrane by washing water, and thereafter, the magnetic flocs stagnating in the vicinity of water surface are attracted and magnetically separated by the magnetic force of a magnet disposed stationary in the vicinity of the water surface, and then transferred to a sludge recovery tank and eliminated by a sludge transfer means. Finally, the sludge may be burned off on a land or on a sea, or may be composted.  
         [0005]     According to the above Patent document, bacteria having vigorous propagating power particularly under appropriate surrounding conditions, e.g., microorganisms such as colon bacilli remain in treated water at several percents of those in raw water, and colon bacilli propagate in a short time under the appropriate surrounding conditions. In a purifying system for life waste water, for example, in a ship in which the treated water is stored for a given period, the water is purified during voyaging of the ship in order to meet an effluent standard for life waste water, but there is a problem that for the period of storage of the treated water in a life waste water tank, colon bacilli in the treated water propagate for a voyaging period to deteriorate the quality of the treated life waste water beyond the effluent standard and as a result, discharging of the treated water becomes unacceptable.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     It is an object of the present invention to provide a filtering and purifying system capable of reducing the concentration of residual possible nutrients to remarkably reduce the propagating function of bacteria.  
         [0007]     The above object is achieved by a filtering and purifying system comprising a production means for producing a product by coagulating matter to be removed in a fluid to be treated, chemically catching and bonding the matter, and a filtering means having an opening size through which the product provided by the production means at a size larger than that of the matter to be removed can not pass. A treating means for at least sterilizing or oxidizing the matter to be removed in the fluid to be treated is provided in the production means.  
         [0008]     The above object is also achieved by a filtering and purifying system comprising a fluid storing means for storing a fluid to be treated, a production means for producing a product by coagulating matter to be removed in the fluid to be treated, chemically catching and bonding the matter, and a filtering means having an opening size through which the product provided by the production means at a size larger than that of the matter to be removed can not pass. A treating means for at least sterilizing or oxidizing the matter to be removed in the fluid to be treated is provided in the fluid storing means.  
         [0009]     Further, the above object is achieved by a filtering and purifying system comprising a production means for producing a product by coagulating matter to be removed in a fluid to be treated, chemically catching and bonding the matter, a filtering means having an opening size through which the product provided by the production means at a size larger than that of the matter to be removed can not pass, and a treated-water storing means for storing treated water filtered by the filtering means. A treating means for at least sterilizing or oxidizing the matter to be removed in the fluid to be treated is provided in the treated-water storing means.  
         [0010]     Furthermore, the above object is achieved by a filtering and purifying system comprising a production means for producing a product by coagulating matter to be removed in a fluid to be treated, chemically catching and bonding the matter, and a filtering means having an opening size through which the product provided by the production means at a size larger than that of the matter to be removed can not be pass. The production means has therein a fluid stirring means for stirring the fluid to be treated, and a treating means for at least sterilizing or oxidizing the matter to be removed in the fluid to be treated is provided in the fluid stirring means.  
         [0011]     Yet further, the above object is achieved by a filtering and purifying system comprising a production means for producing a product by coagulating matter to be removed in a fluid to be treated, chemically catching and bonding the matter, and a filtering means having an opening size through which the product provided by the production means at a size larger than that of the matter to be removed can not pass through the filtering means. A plurality of treating means for at least sterilizing or oxidizing the matter to be removed in the fluid to be treated and a restoring means for restoring reduced sterilizing or oxidizing functions of the treating means are provided in the production means, and at least one or more of the treating means with the sterilizing or oxidizing functions restored function continuously during purifying operation.  
         [0012]     According to the invention, it is possible to provide the filtering and purifying system capable of reducing the concentration of residual possible nutrients and remarkably reducing the propagating function of bacteria.  
         [0013]     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0014]      FIG. 1  is a flow diagram of the filtering and purifying system according to an embodiment of the invention.  
         [0015]      FIG. 2  is a sectional view of a magnetically separating section in the embodiment of the invention.  
         [0016]      FIG. 3  is a sectional view taken along a line A-A in  FIG. 2 .  
         [0017]      FIG. 4  is a flow diagram of the filtering and purifying system according to another embodiment of the invention.  
         [0018]      FIG. 5  is a view for explaining a further embodiment of the present invention.  
         [0019]      FIG. 6  is a view for explaining a still further embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     Embodiments of the invention will be now described with reference to the drawings.  
         [0021]     The first embodiment of the invention will be described with reference to  FIGS. 1, 2  and  3 .  FIG. 2  is an enlarged sectional view of a membrane separator  14  shown in  FIG. 1 , and  FIG. 3  is a sectional view taken along a line A-A in  FIG. 2 .  
         [0022]     Raw water  2  which is water to be treated, for example a life waste water introduced into a ship at a port visit, and from which large refuse of several millimeters has been removed, is stored in a raw water storage tank  1 , for example a life waste water tank in the ship, and the raw water  2  is fed in a predetermined amount to a pipe line  4  by a pump  3 . A magnetic powder such as iron tetroxide, a pH adjuster, a flocculating agent such as an aqueous solution of aluminum polychloride, ferric chloride or ferric sulfate which provides aluminum ion or iron ion, a polymer reinforcing agent and the like are supplied from a seeding agent adjusting device  5  through a conduit  6  into the pipe line  4  and then stirred at a high speed in a stirring tank  7  by a stirring blade  9  driven for rotation by a motor  8 , thereby producing magnetic micro flocs of several hundred micrometers.  
         [0023]     Thereafter, a polymer reinforcing agent or the like is supplied from a polymer agent adjusting device  11  through a conduit  12  into a pipe line  10  and then stirred slowly at a low speed by a stirring blade  15  driven for rotation by a motor  14  in a stirring tank  13 , whereby the magnetic micro-floc groups are entangled and agglomerated by the polymer reinforcing agent to produce a pretreated water  17  containing magnetic flocs  16  (not shown in  FIG. 1 ) having a size on the order of several millimeters.  
         [0024]     A transparent tube for allowing passage of ultraviolet rays therethrough from the side of the atmosphere, for example a glass tube  74 , is immersed into the pretreated water in the stirring tank  13 , and a sterilizing ultraviolet lamp  74  connected to a power source  72  by a wire  73  is inserted into the glass tube  71  to apply ultraviolet rays into the pretreated water. In the stirring tank  13 , the pretreated water is mixed all over by the stirring blade  15  and hence, the ultraviolet rays are applied even to bacteria, e.g., colon bacilli, on the back side of the produced flocs as viewed from the side of the ultraviolet lamp as the flocs move, whereby the pretreated water is sterilized. Here, the pretreated water is mixed for several minutes and hence, is constantly irradiated with the ultraviolet rays. In the stirring tank  13 , polluted particles are taken into the magnetic flocs, whereby the transparency of the pretreated water is increased, and the ultraviolet rays from the ultraviolet lamp are transmittable through the entire region of the pretreated water. Therefore, most of the colon bacilli which have not been taken into the flocs are killed, and the living colon bacilli in the treated water are remarkably decreased. The pretreated water is moved all over to the vicinity of the ultraviolet lamp by the stirring blade and hence, the ultraviolet lamp having a weaker illumination intensity and a smaller power consumption can be used, leading to an effects of reducing the lamp cost and a sterilizing operational cost.  
         [0025]     The pretreated water  17  thus produced is passed through a conduit  18  into a membrane separator  19 . The structure of the membrane separator  19  will be described below with reference to  FIGS. 2, 3 . A net  21  serving as a membrane with openings having an opening size of from several micrometers to several ten micrometers and made of a small-gage wire of stainless steel, a small-gage wire of copper, polyester fibers or the like is mounted on an outer peripheral surface of a rotary drum  20  shown in  FIG. 3 . The pretreated water flows into a water tank  22  and is passed through the net  21  into the drum  20 . At this time, the magnetic flocs  16  in the pretreated water are caught on an inner surface of the net  21 , and the water passed through the net  21  with the magnetic flocs separated therefrom is discharged in the form of purified water through an opening  23  shown in  FIG. 1 , passed through a pipe line  24 , accumulated in the washing water tank  25 , and discharged to outside the system or stored in the life waste water tank in the ship. A power for the pretreated water to pass through the net  21  is a difference in surface level between the pretreated water  17  and the purified water in the drum  20 .  
         [0026]     The colon bacilli in the pretreated water which could not be filtered in the net  21  remain in the treated water, but most of the colon bacilli are dead. Bacteria and organic substances having a size equal to or larger than 0.1 μm in the life waste water have been taken into the magnetic flocs and little remain in the treated water filtered by the net  21 . Thus, as there is only little living colon bacilli remaining in the treated water, and as the amount of nutriments in the treated water has been remarkably decreased, it is possible to substantially prevent the living colon bacilli from being proliferated within a period of storage of the treated water. Therefore, the treated water is note deteriorated, may maintain the water quality which met the discharge water standard at the time of the treatment, and may be discharged to the outside of the ship even after being stored.  
         [0027]     The magnetic flocs  16  are filtered by the net  21  and deposited on its outer surface rotated in a counterclockwise direction as viewed in  FIG. 2 , and exposed in the form of a deposit to the atmosphere above the liquid surface. The purified water in the washing water tank  25  of  FIG. 1  is pressurized and fed through a conduit  27  to a shower pipe  28  by a pump  26 , and shower water is sprayed from apertures to the outer surface of the net  21  from the inner surface side of the net  21 . The magnetic flocs  16  accumulated on the outer surface of the net  21  are peeled off by the shower water, and the surface of the net  21  is regenerated. The magnetic flocs washed off stay on the surface of the pretreated water  17  in the water tank  22 .  
         [0028]     A rotary magnet  29  ( FIG. 1 ) used as a magnetic field generating means for the magnetic separation has a construction in which a plurality of permanent magnet elements  31  are fixed by an adhesive or the like into a plurality of grooves in an outer surface of a rotor  30  ( FIG. 2 ) made of a non-magnetic material and the rotor  30  is rotated at a controlled rotational speed by a motor  32  ( FIG. 3 ).  
         [0029]     On the other hand, as shown in  FIG. 3 , a sludge transferring rotor  33  made of a non-magnetic material and used for transferring the magnetic flocs magnetically separated off is rotated at a control rotational speed through a shaft  34  by a motor  35 . At one end, the shaft  34  is supported on a wall of the water tank  22  by a rotary support  36  having a water-tightness, and at the other end, an outer periphery of the rotor  33  is supported on the wall of the water tank  22  through a rotary support  37  also having a water-tightness, wherein the inside of the rotary support  37  is opened to the atmosphere. The magnet  29  shown in  FIG. 11  is inserted into the inside of the rotor  33  from the side of the rotor  33  opened to the atmosphere, and is placed in proximity of a location where the magnetic floc  16  groups washed off by washing water are staying, i.e., a location closer to the rotary drum.  
         [0030]     In this embodiment, the rotors  33  and  30  are arranged with their axes offset from each other. Although not shown in the figures, the magnet  29  is fixed to a portion of the water tank  22  by bolts or the like, so that it is positioned at a predetermined location. The rotational directions of the rotors  33  and  30  are the same, and the rotors  33  and  30  are rotated in the direction for moving the magnetic floc groups magnetically attracted thereto toward the atmosphere side. The numbers of rotation of the rotors  33 ,  30  may be the same or different. In the case of this embodiment, the rotation speed of the rotor  30  on the magnet side is larger than that of the rotor  33 .  
         [0031]     The magnetic floc  16  groups washed down and staying in the vicinity of the water surface are attracted and moved toward the magnet side by the magnetic field of the magnet  29 , attach to the outer surface of the rotor  33  rotated outside the magnet  29 , and thereafter are exposed to the atmosphere with the rotation of the rotor  33 . A surplus amount of water in the magnetic floc  16  groups flows down the surface of the rotor  33  by gravitation, and the magnetic floc  16  groups are further concentrated. Here, the water content of the magnetic flocs is lowered to about 97%.  
         [0032]     The magnetic floc groups concentrated on the surface of the rotor  33  are moved by the rotation of the rotor  33 . At this time, the axes of the rotors  30 ,  33  get gradually away from the magnet  29 , since they are misaligned from each other, whereby the magnetically attracting force is rapidly decreased as they are more apart from the magnet. The magnetic floc  16  groups are peeled off from the surface of the rotor  33  by a spatula  38  supported on a portion of the water tank  22  to scrape off them, drop into a sludge recovery tank  39  by gravitation, and are collected as a sludge.  
         [0033]     The sludge discharged is introduced through a pipe line  40  into a dewatering device  41  such as a centrifugal separator, a belt press or the like, where the sludge is concentrated into a water content equal to or lower than about 85% enough to prevent water to be leaked from the sludge during transportation of the sludge, or to a water content of a bout 75% enough to permit the activation of microorganisms for decomposing organic substances at the time of composting. The sludge of a high concentration is fed through a pipe line  42  into a sludge tank  43  and stored.  
         [0034]     Treated sewage dewatered in the dewatering device is fed through a pipe line  44  into a sewage treating tank  45 , pressured by a pump  46 , then returned through a pipe line  47  to the raw water tank  1 , and introduced again into the pretreating step. With regard to an operation control unit  48 , a surface level, turbidity, temperature, a pH value and the like of the raw water are detected by a sensor  49 , and the information is transmitted through a signal line to the operation control unit  48 . Amounts of chemicals (the pH adjuster, the magnetic powder, the flocculating agent) to be added, which are optimal to produce good magnetic flocs, are calculated based on the information using an optimal amount calculating program previously inputted, and the resulting control information is transmitted via a signal line  51  to a chemical agent tank  5  for addition of the optimal amounts.  
         [0035]     Further, a number of rotation of the stirring motor and a time period of staying in the stirring tank are calculated in the operation control unit  48 , and the resulting control information is transmitted via a signal line  52  to the motor  8  to rotate the stirring blade  9  at the optimum rotation speed and is transmitted via a signal line  53  to control a discharge rate of the pump  3  which decides the staying time in the stirring tank. Furthermore, an adding amount of a chemical (high molecular polymer) optimal to produce good magnetic flocs is calculated with the optimal amount calculating program previously inputted, and the resulting control information is transmitted via a signal line  54  to the chemical agent tank  11  to add the optimum amount. At the same time, a number of rotation of the stirring motor is calculated in the operation control unit  48  and transmitted via a signal line  55  to the motor  14  to rotate the stirring blade  15  at the optimum rotation speed.  
         [0036]     In the membrane separator  19 , on the other hand, a liquid level of the pretreated water  17  in the water tank  22  is detected by a sensor  56 , and the information is transmitted via a signal line  57  to the operation control unit  48 . An optimum number of rotation of the rotary drum  20  and an appropriate rate of recovering the magnetic floc  16  groups are calculated based on the information using the optimal amount calculating program previously inputted, so that the liquid level of the pretreated water is positioned at a substantial central point of the location of placement of the magnet  29 , i.e., a point at which the average value of the magnetic field generated by the magnet  29  is maximum, and the resulting control signals are transmitted via a signal line  58  to a motor (not shown) for rotating the rotary drum and via a signal line  59  to the motor  35 , thereby controlling the motors at the optimum rotation speeds.  
         [0037]     As can be seen from the above description, as a result of purifying the raw water such as the life waste water with the purifying system of this embodiment, the colon bacilli in the pretreated water which could not be filtered by the filter pass into the purified, treated water, but most of the colon bacilli are dead. In addition, bacteria and organic substances of a size equal to or larger than 0.1 μm in the life waste water have been taken into the magnetic flocs and hence, little remain in the treated water filtered by the filter. Therefore, the living colon bacilli scarcely remain in the treated water, nutriments in the treated water have been remarkably decreased and hence, it is possible to substantially prevent the living colon bacilli from being proliferated within a period of storage of the treated water. Thus, the quality of the treated life waste water is not deteriorated, and the effluent standard for the water quality satisfied at the time of the treatment can be maintained, leading to an effect that the treated water can be stored and then discharged to the outside of the ship.  
         [0038]     In this embodiment, the glass tube  71  transparent to permit the transmission of ultraviolet rays therethrough from the atmosphere is inserted into the pretreated water in the stirring tank  13 , and the sterilizing ultraviolet lamp  74  is inserted into the glass tube  71 , whereby the ultraviolet rays can be emitted into the treated water. In the stirring tank  13 , the pretreated water is mixed all over by the stirring blade  15 . Therefore, the ultraviolet rays are applied even to colon bacilli on the back side of the produced flocs as viewed from the side of the ultraviolet lamp with the movement of the flocs, and the colon bacilli are killed. The mixing in the stirring tank  13  is conducted for a period of several minutes, and during this time, the ultraviolet rays are constantly applied to the pretreated water. Therefore, the sterilizing time is sufficient, a sterilizing effect is produced sufficiently even by the ultraviolet lamp having a smaller illumination intensity, and thus, most of the colon bacilli which have not been taken into the flocs are killed, leading to an effect of remarkable decreasing of the number of the living colon bacilli in the treated water.  
         [0039]     Although the ultraviolet lamp  74  is disposed in the stirring tank  13  in this embodiment, it may be disposed in the stirring tank  7 , the membrane separator  19  or the washing water tank  25 , and even in this case, a similar effect is obtained.  
         [0040]     In this embodiment, when the outer surface of the glass tube  71  is fouled by the treated water, resulting in a reduction in transmission of the ultraviolet rays, then the transmission can be restored by taking the glass tube  71  out of the stirring tank  13 , washing and removing the dirt. The washing and removal may be carried out automatically in the stirring tank  13 , although not shown in the figures.  
         [0041]     The glass tube  71  and the ultraviolet lamp may be disposed in any other place as long as they do not interfere with the rotation of the stirring blade, and a plurality of glass tubes may be disposed between stirring blades, although not shown in the figures. In addition, a plurality of types of ultraviolet lamps having different frequencies and wavelengths effective for a plurality of microorganisms respectively may be disposed, although not shown in the figures.  
         [0042]     The second embodiment of the invention is shown in  FIG. 4 . This figure is different from  FIG. 1  in that in place of the ultraviolet lamp  74  provided for sterilizing the colon bacilli, a predetermined amount of a chemical in a chemical agent tank  75 , for example the chemical for producing hydrogen peroxide, is added through a pipe line  76  into the stirring tank  13 . Hydrogen peroxide is produced in the pretreated water in the stirring tank  13 , by the power of active oxygen, colon bacilli which have not been taken into the magnetic flocs in the pretreated water are killed and very fine organic substances are oxidized and decomposed.  
         [0043]     According to this embodiment, the mixing in the stirring tank  13  is conducted for a period of several minutes and during this time, the pretreated water is constantly mixed. The hydrogen peroxide is therefore spread all over in the pretreated water with no unevenness of concentration caused. Further, there is a sufficient sterilizing time. Therefore, even if the amount of chemical added is controlled to the minimum, a sufficient sterilizing effect is obtained, and most of the colon bacilli in the pretreated water which have not been taken into the flocs are killed, leading to an effect of remarkable decreasing of the number of the living colon bacilli in the treated water.  
         [0044]     In this embodiment, parts of vary fine organic substances which have not been taken into the magnetic flocs in the pretreated water are oxidized and decomposed by the oxidizing force of the hydrogen peroxide. Therefore, the residual amount of the organic substances in the treated water as nutriments for the bacteria is further decreased, leading to a further effect of preventing proliferation of the living colon bacilli in the treated water.  
         [0045]     In this embodiment, the sterilizing chemical is added into the treated water in the stirring tank  13 , it may be added into the raw water in the raw water tank  1 , into the pretreated water in the stirring tank  7 , into the pretreated water or the treated water in the membrane separator  19 , or into the treated water in the washing water tank  25 , and in this case, a similar effect is obtained.  
         [0046]     Although the above description has been made on the cases where the bacterium-killing treatment and the organic substance-oxidizing treatment have been carried out by providing the ultraviolet lamp and by pouring the chemical from the sterilizing agent tank, substances functioning for sterilizing and oxidizing may be produced or added by providing any suitable device other than the ultraviolet lamp, such as an ozone generating device, an electrolytic hypochlorite-generating device or a ultrasonic wave-generating device, and in this case, a similar effect is obtained.  
         [0047]     The third embodiment of the invention is shown in  FIG. 5 . Difference in this figure from the structure of the stirring tank  13  in  FIG. 1  is an arrangement in which a plurality of glass tubes each having a colon bacillus-killing ultraviolet lamp  74  therein are provided, and each glass tube is equipped with an elevator for moving it upwards and downwards between a location in the water and the water surface.  
         [0048]     The glass tubes  77 ,  78  with the colon bacillus-killing ultraviolet lamp  74  mounted therein are provided within a stirring tank  13  shown in the figure. The glass tubes  77 ,  78  are supported by rods  79 ,  80 , respectively, which are movable between positions in the pretreated water in the stirring tank  13  and positions in the atmosphere above the water surface by elevators  81 ,  82 , respectively. The movement of the rods  79 ,  80  is controlled by controlling the normal and reverse rotation of, for example, gears  83 ,  84  in the elevators  81 ,  82 .  
         [0049]     An outer surface of the glass tube  78  arranged within the stirring tank  13  shown in the figure may be fouled by the pretreated water after operation for a long period of time, thereby decreasing its transmission for ultraviolet rays and reducing the sterilizing performance for killing bacteria in the pretreated water around an outer periphery of the glass tube  78 . Ultraviolet ray-transmission sensors  85 ,  86  for detecting a reduction in the transmission of the ultraviolet rays are mounted on the outer peripheries of the glass tubes  77 ,  78  at small distances apart from the glass tubes.  
         [0050]     When the dirt of the outer surfaces of the glass tubes is detected by the ultraviolet ray-transmission sensor  85 ,  86 , this is transmitted through signal lines  87 ,  88  to a control unit (not shown), and the fouled glass tubes are moved toward the atmosphere above the water surface by the elevators  81 ,  82 .  FIG. 5  shows the case where the glass tube  78  has been moved.  
         [0051]     The fouling of outer surfaces, i.e., light-receiving surfaces of the ultraviolet ray-transmission sensors  85 ,  86  is removed automatically by small wipers (not shown) or the like, respectively.  
         [0052]     The outer surface of the glass tube  78  is washed automatically during its movement by a washer  89  which is adapted to wash the glass tube outer surface, for example, with water or an acidic washing liquid and a brash, and a waste liquid after the washing is returned through a pipe line  90  to the raw water tank  1 . During this movement, the ultraviolet lamp  74  is turned off.  
         [0053]     The glass tube  78  washed stands by as it is, and after the outer surface of the glass tube  77  is fouled and a predetermined level of fouling is detected by the ultraviolet ray-transmission sensor  85 , the glass tube  78  is replaced for the glass tube  77  and inserted into the stirring tank  13 , and the ultraviolet lamp is turned on.  
         [0054]     On the other hand, the glass tube  77  is moved upwards toward the atmosphere with the outer surface of the glass tube  77  being automatically washed during the movement, and the waste water resulting from the washing is returned through a pipe line  91  to the raw water tank  1 .  
         [0055]     According to this embodiment, any of the ultraviolet lamps  74  in the glass tubes may be used to continuously kill bacteria in the pretreated water  17 , having an effect that the pretreated water can be sterilized without stopping the mixing operation of the stirring tank  13 .  
         [0056]     The fourth embodiment of the invention is shown in  FIG. 6 . Difference in this figure from the structures of the stirring tanks  7 ,  13  in  FIG. 1  is arrangements which will be described below. The blade-type stirring tank  7  is replaced by the arrangement comprising a mixing tube  93  having a ribbon-shaped turbulent flow promoting plate  92  mounted in a flow passage, a pipe line  94  and a mixing tube  95 , and the blade-type stirring tank  13  is replaced by the arrangement comprising mixing tubes  99 ,  100  which are in communicate with each other through a pipe line  101  and which are each equipped in flow passages with doughnut-type ribbon-shaped turbulent flow promoting plates  96  and glass tubes  97 ,  98  each having a ultraviolet lamp  74  mounted therein.  
         [0057]     In addition, as a standby for washing the glass tubes, a mixing tube  103  equipped, in its flow passage, with a doughnut-type ribbon-shaped turbulent flow promoting plate  96  and a glass tube  102  having a ultraviolet lamp  74  mounted therein, is provided in parallel. This is put in communication with the other mixing tubes through a pipe line  104  and valves  105 ,  106  as well as a pipe line  107  and a valve  108 , and further connected to a pipe line  10  and a pipe line  18  through a pipe line  109  and a valve  110  as well as a valve  111  and a pipe line  112 .  
         [0058]     The turbulent flow promoting plates  92 ,  96  in the mixing tubes mix and stir the pretreated water within the mixing tubes with an effect similar to that provided by the stirring blade within the mixing tank, and bacteria in the pretreated water are killed in a manner similar to that in the mixing tank  13  by the application of ultraviolet rays from the ultraviolet lamps  74  in the mixing tubes  99 ,  100  and  103 . The turbulent flow promoting plates  96  provided in the mixing tubes  99 ,  100  and  103  are stationary, and flowing fluid is stirred and mixed by the disturbance provided by the ribbon-shaped turbulent flow promoting plates.  
         [0059]     The outer surfaces of the glass tubes  97 ,  98  and  102  disposed in the mixing tubes  99 ,  100  and  103  are fouled with the operation and need washing.  FIG. 16  shows a case where the glass tube  98  within the mixing tube  100  is washed.  
         [0060]     In this case, the valve  113  in the pipe line  10  is opened, the valve  105  is closed, the valve  108  is opened, the valve  106  is closed, the valve  110  is closed, and the valve  111  is opened. In this case, the pretreatment is carried out by the mixing tubes  99 ,  103 . The glass tube  98  in the mixing tube  100  which is to be washed is moved by an elevator (not shown), and the outer surface of the glass tube  98  is washed automatically by a washer  121  having air-tightness. The mixing tubes  99 ,  103  are provided with washers  114 ,  115 , respectively. Washing water flows through pipe lines  116 ,  117 ,  118  and  119  back to the raw water tank  1 .  
         [0061]     After the washing of the outer surface of the glass tube  98 , it is moved into the mixing tube  100  by the elevator (not shown), the ultraviolet lamp is turned on, the valves  108 ,  110  and  111  are closed, while the valve  106  is opened, and the ultraviolet lamp  74  in the mixing tube  103  is turned off.  
         [0062]     When the glass tube  97  in the mixing tube  99  is to be washed, the valves  113  and  111  are closed, while the valves  105 ,  110  and  120  are opened, the ultraviolet lamp  74  in the mixing tube  103  is turned on, while the ultraviolet lamp  74  in the mixing tube  99  is turned off, the glass tube  97  is moved by an elevator (not shown), and the outer surface of the glass tube  97  is washed automatically by the washer  114  having air-tightness.  
         [0063]     After the washing of the glass tube  97 , it is moved into the mixing tube  99  by the elevator (not shown), the ultraviolet amp is tuned on, the valves  113  and  106  are opened, while the valves  105 ,  110  and  120  are closed, and the ultraviolet amp  74  in the mixing tube  99  is turned off. To wash the glass tube  102  in the standby mixing tube  103 , the valves  105 ,  108 ,  110  and  111  are closed, the ultraviolet amp  74  in the mixing tube  103  is turned off, the glass tube  102  is moved by an elevator (not shown), and the outer surface of the glass tube  102  is washed automatically by the washer  115  having air-tightness. After the washing, the glass tube  102  is moved into the mixing tube  103  by the elevator (not shown).  
         [0064]     In this embodiment, the pretreated water is mixed all over in meandering flows generated by the turbulent flow promoting plates in the mixing tubes. Therefore, ultraviolet rays from the ultraviolet lamps in the central glass tubes are applied all over to the pretreated water during the mixing and stirring, and the bacteria in the pretreated water are killed reliably.  
         [0065]     This embodiment has been described above as using the doughnut-type ribbon-shaped plate as the turbulent flow promoting plate, but porous plates may be placed as the turbulent flow promoting plates at a predetermined distance in a direction of flowing of the pretreated water. Also in this case, a similar effect is obtained.  
         [0066]     According to this embodiment, the ultraviolet lamps  74  are placed in the mixing tubes and can be used to continuously kill the bacteria in the pretreated water  17 . Therefore, even when a mixing tube is used and the outer surface of a glass tube having a infrared lamp mounted therein is fouled, there is an effect that the pretreated water can be sterilized without stopping the mixing in the mixing tube. Although the above embodiments have been described on the case where the water to be purified is the life waste water in the ship, the water to be purified may be ballast water containing plant plankton or animal plankton or bacteria such as cholera germ, colon bacilli and intestine micrococcus and even in this case, a similar effect is obtained.  
         [0067]     It should be further understood by those skilled in the art that although the foregoing description has been made on the embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.