Abstract:
The present invention provides a method of removing ozone remaining in water by separating residual ozone which remains in water after ozone is melted in the water and kills microorganisms in the water including the steps of storing water containing the residual ozone in a pressure tank, supplying the pressure tank with compressed air, generating coarse bubbles larger than the residual ozone existing in water in the form of micro bubbles in pressurized condition, making the residual ozone in the form of micro bubbles adhere to the coarse bubbles, separating the residual ozone from water as the coarse bubbles go up, and discharging the micro bubbles from the pressure tank. 
     Accordingly, the present invention provides a method of removing ozone remaining in water to remove ozone remaining in water inexpensively and efficiently.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of removing ozone remaining in water. More specifically, the present invention relates to a method of removing ozone which remains in the form of micro bubbles in water such as ballast water after killing microorganisms mixing in water with ozone, offering a solution to the problem of corrosion of ballast tanks by ozone. 
       BACKGROUND 
       [0002]    Cargo ships carrying crude oil, etc are provided with ballast tanks to balance their body during navigation. 
         [0003]    Usually, the ballast tanks are filled with ballast water when crude oil, etc are not on-board, while the ballast water is discharged before crude oil, etc are loaded. 
         [0004]    Ballast water is necessary for safe navigation of ships, and it is usually taken from sea water in the port where cargo handling is undertaken. The total quantity of ballast water used in the world is estimated at 3 to 4 billion tons a year. 
         [0005]    Ballast water contains aquatic organisms which inhabit in ports where the ballast water is drawn, and the aquatic organisms are conveyed to other countries as the ships move. Consequently, destruction of ecological system is increasingly serious that alien organism species take the place of indigenous species in the sea area. 
         [0006]    As seriously considered the above background, a diplomatic conference at the International Maritime Organization (IMO) adopted the International Convention for the Control and Management of Ships&#39; Ballast Water and Sediments to make the obligation of implementing ballast water control by use of any ballast water treatment apparatus be applied to ships to be built from 2009 onward. 
         [0007]    In addition, the convention prescribed the ballast water discharging standard as shown in Table 1: 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Ballast Water 
                   
               
               
                 Items 
                 Quality Criteria 
                 Size 
               
               
                   
               
             
             
               
                 Aquatic Organisms 
                 10 unit/ml 
                 10-50 μm 
               
               
                 Aquatic Organisms 
                 10 unit/m 3   
                 50 μm or more 
               
             
          
           
               
                 Indicator 
                 
                   Escherichia Coli 
                 
                 250 cfu/100 ml 
                 / 
               
               
                 Microbes 
                 
                   Vibrio cholerae 
                 
                 1 cfu/100 ml 
                 / 
               
               
                   
                 (O1 and O139) 
               
               
                   
                 Genus  Enterococcus   
                 100 cfu/100 ml 
                 / 
               
               
                   
               
             
          
         
       
     
         [0008]    Accordingly, it is now a matter of great urgency to develop a sterilization and/or elimination technology in the ballast water which can solve the above problem. 
         [0009]    Conventionally, a technology for sterilization by means of injecting ozone into ballast water in parallel with injecting steam and further generating micro bubbles of ozone to promote formation of hydoxyradicals to reduce consumption of ozone has been offered, as seen in Unexamined Patent Application Publication No. 2004-160437(JP). 
       SUMMARY 
       [0010]    Ozone is mixed into ballast water to perform sterilization, as a result, ozone left unused for sterilization remains in the form of micro bubbles. When water containing this residual ozone is poured into a ballast tank, the residual ozone causes a problem of corroding the ballast tank, transfer piping, etc. 
         [0011]    In case of building a new ship it may be considered to use corrosion-resistant materials for ballast tanks, transfer piping, etc to solve this problem; however, it will cause a problem of increasing shipbuilding costs remarkably. In case of an existing ship it may be considered to apply corrosion-resistant paint or corrosion-resistant rubber lining, etc.; however it will also cause a problem of higher costs. 
         [0012]    On the other hand, if the water containing residual ozone is left alone at atmospheric pressure for dozens of minutes, the residual ozone will separate from the water and escape into the air. However, in order to do so, it will be necessary to have a tank of large volume sufficient for leaving the water containing residual ozone alone before pouring it into a ballast tank. It will be very costly and impractical. 
         [0013]    Furthermore, it may be considered to hold the water containing the residual ozone in a tank for a time to accelerate deaeration of the residual ozone by reducing the pressure in the tank to remove the residual ozone; however, it will require a transfer pump as well as a pressure-reducing pump, causing a problem of higher costs. 
         [0014]    It is to be noted that holding ozonized water will cause a problem of corrosion by residual ozone; therefore, the problem is not peculiar to ballast water, but common to any usual water. 
         [0015]    The object of the present invention is to provide a method of removing ozone remaining in water to remove ozone remaining in water inexpensively and efficiently. 
         [0016]    Other objects of the present invention will be disclosed in the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Various aspects of the present disclosure will be or become apparent to one with skill in the art by reference to the following detailed description when considered in connection with the accompanying exemplary non-limiting embodiments, wherein: 
           [0018]      FIG. 1  shows an example of an apparatus for implementing the method of removing ozone remaining in ballast water embodying the present invention; 
           [0019]      FIG. 2  is an illustration of how micro bubbles of ozone are separated and removed; 
           [0020]      FIG. 3  shows an example of another apparatus for implementing the method of removing ozone remaining in water embodying the present invention; 
           [0021]      FIG. 4  shows an example of an apparatus for melting ozone in ballast water; 
           [0022]      FIG. 5  is a cross-sectional view along line X-X in  FIG. 4 ; 
           [0023]      FIG. 6  shows an example of device to reduce the quantity of ozone to be mixed into ballast water; 
           [0024]      FIG. 7  shows another example of device to reduce the quantity of ozone to be mixed into ballast water; and 
           [0025]      FIG. 8  shows an example of a jet generating device. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    A pressure tank  1  in  FIG. 1  stores ballast water  100  sterilized with ozone. 
         [0027]    The ballast water  100  is water picked to be poured into a ballast tank (not shown) of a ship such as a tanker. 
         [0028]    Sea water is usually used as the ballast water  100 . In order to pour the ballast water  100  into the ballast tank, sea water is sucked with a pump  2  and sent to the pressure tank  1  through a pipe  3 . 
         [0029]    A filter (not shown) may be installed between the pressure tank  1  and the pump  2  to remove litter and trash. 
         [0030]    The ballast water  100  sucked with the pump  2  is mixed with ozone injected in the process of its transfer to the pressure tank  1  through the pipe  3 . The injected ozone is melt into the ballast water and kills microorganisms (e.g. aquatic organisms, colon bacillus, etc. as shown in Table 1). 
         [0031]    There is no specific limitation placed on methods of melting ozone into the ballast water  100 . 
         [0032]      FIG. 1  shows an embodiment of melting ozone into the ballast water  100  by use of a static mixer  4  capable of mixing gas and liquid. 
         [0033]    The static mixer  4  is supplied with the ballast water  100  and ozone. Ozone is fed from an ozonizer  5  through an ozone injection tube  6 . The ballast water  100  and ozone are mixed each other in the static mixer  4 , and ozone is instantly mixed with and melted into the ballast water. As a result, microorganisms in the ballast water  100  are killed by ozone in a few seconds. 
         [0034]    The static mixer  4  is preferably such a mixer as is small in pressure loss and excellent in mixing efficiency. 
         [0035]    An aeration pipe  7  is equipped with at the lower part of the pressure tank  1 . The aeration pipe  7  is connected to a compressor  8 , which is an example of compressed air supply means through a pipe  9 . The pipe  9  has a regulating valve  10  which controls the air pressure from the compressor  8 . Driving the compressor  8 , compressed air controlled a predetermined pressure is supplied to the aeration pipe  7 . 
         [0036]    Numeral  11  is an exhaust pipe  11 , providing at the upper part of the pressure tank  1 , which discharges exhaust gas containing the residual ozone separated from the ballast water  100 . The exhaust pipe  11  has a pressure-regulating valve  12  that controls the inner pressure of the pressure tank  1 . 
         [0037]    Numeral  13  is a pressure sensor that senses the inner pressure of the pressure tank  1 , and transmits signals to control the opening and closing of the pressure-regulating valve  12  to regulate the inner pressure of the pressure tank  1  at a predetermined pressure. 
         [0038]    Numeral  14  is a transfer pipe, providing at the lower part of the pressure tank  1 , which transfers the ballast water  100  rid of the residual ozone to the ballast tank (not shown). The transfer pipe  14  is equipped with an on-off valve  15 . 
         [0039]    The pressure tank  1  can be equipped inside with an agitator  16 , if necessary. The agitator  16  is driven by a motor  17 . 
         [0040]    A method of removing residual ozone from the ballast water  100  in the pressure tank  1  is then described as follows: 
         [0041]    The inner pressure of the pressure tank  1  is maintained at a certain level by the pressure of the pump  2  through regulation by the pressure-regulating valve  12 . 
         [0042]    The ballast water  100  in the pressure tank  1  contains the residual ozone not used for sterilization in the form of micro bubbles  300 , as shown in  FIG. 2 . It is because ozone is injected into the ballast water  100  excessively since it is not realistic to inject ozone in the quantity corresponding to the quantity of microorganisms in water subject to treatment at the ratio of 1:1 to meet the regulatory standards perfectly. 
         [0043]    Most of the ozone melt in the ballast water  100  is used to kill microorganisms and does not corrode ballast tanks, etc. However, surplus ozone is not used for sterilization and is left in the ballast water  100  in the size of micro bubbles  300  that is 0.5 μm to 500 μm. The ozone remaining in the form of these micro bubbles  300  causes the problem of corroding ballast tanks, etc. 
         [0044]    In experiments conducted by the present inventors, if the inner pressure of the pressure tank  1  is, for example, about 0.3 MPa (3 kgf/cm 2 ), the ozone remaining in the ballast water  100  takes a form of micro bubbles  300  of about 50 μm. 
         [0045]    While the higher the inner pressure of the pressure tank  1  is, the finer the micro bubbles  300  become, the size of the micro bubbles  300  does not become larger than about 50 μm if the inner pressure of the pressure tank  1  is maintained at the level as above-mentioned. 
         [0046]    High-pressure air is sent by means of the drive of a compressor  8  through the pipe  9  to the aeration pipe  7  in which ozone remains in the form of micro bubbles  300  in pressurized condition. This generates coarse bubbles  200  larger than the micro bubbles  300  contained in the ballast water  100  from the aeration pipe  7 . These coarse bubbles  200  go up through the ballast water  100  because of high buoyancy. 
         [0047]    Since the inside of the pressure tank  1  is kept in pressurized condition, the micro bubbles  300  in the ballast water  100  adhere to the sphere of the coarse bubbles  200  as the coarse bubbles  200  go up through the ballast water  100  as shown in  FIG. 2 . 
         [0048]    That is to say, the present invention ensures that the coarse bubbles  200  larger than the micro bubbles  300  contained in the ballast water  100  are generated in the pressure tank  1  under pressurized condition and the micro bubbles  300  adhere to the coarse bubbles  200  and separate from the ballast water  100 . 
         [0049]    The size (diameter) of the coarse bubbles  200  is preferably 10 to 100 times as large as that of the micro bubbles  300  in the ballast water  100 . If, for example, the size of the micro bubbles  300  is about 50 μm as abovementioned, the size of the coarse bubbles  200  is preferably 500 μm to 5 mm. 
         [0050]    The size of the coarse bubbles  200  can be adjusted by adjusting the pressure of the compressor  8  or the construction of the aeration pipe  7 . 
         [0051]    If the pressure sensor  13  detects the inner pressure of the pressure tank  1  having reached a predetermined pressure, it transmits a signal to open the pressure-regulating valve  12 . This signal regulates the travel of the pressure-regulating valve  12 . In this way, the exhaust gas (O 2 , O 3 , N 2 ) containing the residual ozone separated from the ballast water  100  by the coarse bubbles  200  is discharged outside through the exhaust pipe  11 . The pressure tank  1  is preferably supplied at this point with compressed air so that the exhaust gas can be discharged more easily. 
         [0052]    The following is a preferable example of conditions for pressurizing the pressure tank  1 : 
         [0053]    Let P 1  be the pressure at the inlet of the water from the pipe  3  connected the pressure tank  1 , P 2  be the pressure at the inlet of the air from the pipe  9  and P 3  be the set pressure of the pressure-regulating valve  12 . P 1  is 0.02-0.7 MPa (0.2-7 kgf/cm 2 ), P 2  is 0.01-0.7 MPa (0.1-7 kgf/cm 2 ) and P 3  is 0.01-0.6 MPa (0.1-6 kgf/cm 2 ). P 1  and P 2  are preferably identical each other in substance or P 2  is preferably set to be 0.01-0.2 MPa (0.1-2 kgf/cm 2 ) higher than P 1 . P 3  is preferably set to be identical to or lower than P 1  or P 2 . 
         [0054]    More specifically, if P 1  is set at about 0.3 MPa (3 kgf/cm 2 ), P 2  is set at about 0.4 MPa (4 kgf/cm 2 ) and P 3  is set at about 0.3 MPa (3 kgf/cm 2 ), the pressure tank  1  is pressurized at the pressure of P 2 . As P 2  is set higher than the set pressure of P 3 , the pressure-regulating valve  12  opens under the control of the pressure sensor  13 , and exhaust gas containing residual ozone is discharged through the exhaust pipe  11 . On-off control of opening and closing of the pressure-regulating valve  12  makes it possible to discharge exhaust gas from the exhaust pipe  11  continuously. 
         [0055]    While high-pressure air is sent to the aeration pipe  7 , the ballast water  100  is preferably agitated moderately by rotating the agitator  16  to accelerate contact of the coarse bubbles  200  with the micro bubbles  300  in the ballast water  100 . 
         [0056]    The high-pressure air from the compressor  8  may also be sent to the pressure tank  1  from the pipe  3  in whole or in part through the pipe  18 . 
         [0057]    In the present invention, ozone remaining in the pressure tank  1  can be removed continuously. Since the pressure tank  1  is in pressurized condition, no other pump is required to transfer the ballast water  100  rid of the residual ozone to the ballast tank (not shown). 
         [0058]    In the present invention, the time required for removing the residual ozone is extremely short since high-pressure air is sent from the aeration pipe  7  in pressurized condition. In the present invention, the residual ozone is removed in 1 to 5 minutes of processing. Therefore, the required retention time of the ballast water  100  in the pressure tank is within the range of only 1 to 5 minutes. 
         [0059]    Measures is preferably taken to prevent shortcutting of the ballast water  100  yet to be rid of residual ozone in the pressure tank  1  in order to allow continuous removal of residual ozone in the pressure tank  1  and continuous transfer of the ballast water  100  rid of residual ozone to the ballast tank. 
         [0060]    A device of preventing the shortcutting can be constituted by a partition plate  19  which stands from the bottom of the pressure tank  1 , as shown in  FIG. 3 . The inside of the pressure tank  1  is divided into two chambers. The two chambers join each other above the partition plate  19 . The ballast water  100  is rid of residual ozone by the high-pressure air sent from the aeration pipe  7  in the one chamber, then transferred to the other chamber over the partition plate  19 . The transfer pipe  14  transfers the ballast water  100  rid of the residual ozone in the latter chamber to the ballast tank. 
         [0061]    Furthermore, in the present invention, it is possible to adopt a discrete treatment (batch-type treatment), if necessary. 
         [0062]    Then, another embodiment for melting ozone in the ballast water  100  in the pipe  3  is described as follows: 
         [0063]      FIG. 4  shows an apparatus which melts ozone into ballast water and  FIG. 5  is a cross-sectional view along line X-X in  FIG. 4 . 
         [0064]    In this embodiment, the tip of the ozone injection tube  6  is inserted into the pipe  3 . The ozone injection tube  6  jets ozone into the ballast water  100  in the pipe  3  from a nozzle  61  mounted on an L-shaped tip. 
         [0065]    A screw-propeller  20  is installed on the upstream side of the ozone injection tube  6  in the pipe  3  for generating whirlpools. The screw-propeller  20  rotates at high rates of 3000-6000 rpm, for example, to generate high-speed whirlpools  400  in the ballast water  100  flowing in the pipe  3 . 
         [0066]    The drive shaft  21  of the screw-propeller  20  passes through the pipe wall of the pipe  3  which bends in the shape of L. The drive shaft  21  rotates by means of a motor or an engine (not shown). 
         [0067]    A turbulent flow generating device is installed on the downstream side of the ozone injection tube  6  in the pipe  3 . This turbulent flow generating device can be represented by the static mixer, etc. An example of it is shown in  FIG. 5 . The turbulent flow generating device is constituted by a plurality of plates (six plates are shown in  FIG. 5 ) or rod-shaped bodies  22  ( 22   a ,  22   b ,  22   c ,  22   d ,  22   e  and  22   f ) which are arranged spaced at predetermined intervals on an imaginary spiral line  23  drawn on the inner surface of the pipe  3 . 
         [0068]    The space L in the direction of the shaft line O of two plates or rod-shaped bodies  22  adjoining each other is related to the inside diameter D of the pipe  3  or the velocity of the ballast water  100 , etc. and is preferably within the range of 10-50 mm and more preferably 20-30 mm. The space L being beyond the said range, the turbulent flow will not occur easily. 
         [0069]    The plates or rod-shaped bodies  22  are slightly shorter than the radius of the pipe  3  and stand upright toward the shaft line O of the pipe  3  on the inside wall surface of the pipe  3 . 
         [0070]    The plates or rod-shaped bodies  22  are formed to have an oval cross section. The plates or rod-shaped bodies  22  are so mounted on the inside wall surface of the pipe  3  that the direction of the long axis of the oval may face to the circumference of the pipe  3 . The oval cross section of the plates or rod-shaped bodies  22  promotes shearing whirlpools  400  which rotate spirally. 
         [0071]    Ozone jetted out from the nozzle  61  of the ozone injection tube  6  forms small bubbles and gets caught in the spiral whirlpools  400 . 
         [0072]    The spiral whirlpools  400  involving ozone crash against the plurality of plates or rod-shaped bodies  22  and are agitated violently. As a result small bubbly ozone turns to micro bubbles and are mixed evenly and melt in the ballast water  100 . 
         [0073]    The plates or rod-shaped bodies  22  may be so arranged as to traverse the inside of the pipe  3 . 
         [0074]    In addition, the plates or rod-shaped bodies  22  may be provided with a convex and a concave at their rear end for reducing resistance so that friction resistance may be reduced greatly. This will result in reducing required motor power. 
         [0075]    In the present invention, a device for reducing ozone to be mixed in the ballast water  100  is preferably provided. 
         [0076]      FIG. 6  shows an example of the device. Numeral  24  is a compressor which is used as an example of an air supply device. The air supplied from the compressor  24  is mixed in the ballast water flowing in the pipe  3  on the downstream side of the location where ozone is fed from the ozonizer  5  through the ozone injection tube  6 . 
         [0077]    Numeral  25  is a micro-bubble generator. The micro-bubble generator  25  feeds ballast water mixed with air and ozone and generates micro bubbles. 
         [0078]    The micro-bubble generating mechanism being observed, focusing only on the air out of the air and ozone fed to the ballast water, OH −  on the interface with bubbles increases and charges the interface negatively. This OH −  is free radical species of active oxygen and has oxidative and microbicidal functions. In this way microorganisms in the ballast water are killed. OH −  is generated in large quantity when the micro-bubbles crush. 
         [0079]    That is, in this embodiment, generated micro-bubbles show sterilization effect through interaction between electrifiability of micro-bubbles and crush of micro-bubbles. This allows reduction of the quantity of ozone to be mixed. The quantity of ozone to be mixed can be within the range of 1-20 ppm for the ballast water. 
         [0080]    The micro-bubble generator  25  is preferably represented by a static mixer, which does not require power source. 
         [0081]    The pressure loss of the micro-bubble generator  25  is preferably within the range of 0.2-0.3 MPa (2-3 kgf/cm 2 ). 
         [0082]      FIG. 7  shows another example of devices which reduce the quantity of ozone to be mixed in the ballast water  100 . 
         [0083]    In  FIG. 7 , numeral  26  is a jet generating device, which is installed on the pipe  3  between the static mixer  4  and the pressure tank  1 . 
         [0084]    The jet generating device  26  consists of a water jet nozzle  27  and an impact plate  28 , as shown in  FIG. 8 . 
         [0085]    The jet nozzle  27  has preferably a shape of having a squeezing part  271  and an expanding part  272 . The ballast water flowing in the pipe  3  with ozone injected therein is once squeezed in the squeezing part  271  and then jetted in the expanding part  272 . The jet generating device  26  generates jet in this way. The squeezing part  271  is the origin of the jet. 
         [0086]    The impact plate  28  is formed in a smaller shape than the inside diameter of the pipe  3 , for example in quadrangle and arranged in the pipe  3  at a position where the water which has passed the expansion part  272  can crash against the impact plate  28 . A clearance  281  is formed around or above or below (or on the right or left of) the impact plate  28  to allow water to pass between the inside wall of the pipe  3  and the impact plate  28 . Numeral  29  is a reducer. 
         [0087]    The distance between the squeezing part  271  and the impact plate  28  is set as appropriate so that eradication can be realized effectively by means of cavitation and impact. 
         [0088]    This jet generating device  26  generates jet by means of the water jet nozzle  27  and gives a sharp pressure change to the ballast water flowing in the pipe  3 . Thus, this jet generating device  26  ensures that cavitation generates in the ballast water and, therefore, microorganisms such as plankton are destroyed and eradicated. 
         [0089]    The ballast water is transferred from the pipe  3  to the water jet nozzle  27  by the pump  2  at the rate of 20-30 m/sec and crashes against the impact plate  28 . High pressure generated by the jet, sharp pressure change generated by negative pressure and impactive force and frictional force generated by crash against the impact plate  28  destroy pneumatophores or cell walls of microorganisms such as plankton contained in the ballast water and eradicate them. Required quantity of ozone can be decreased in this way. 
         [0090]    The jet generating device  26  is not limited to the embodiment. For example, a plurality of water jet nozzles may be arranged face to face or at an angle to increase the cavitation effect. Besides, the surface shape of the impact plate  28  may be convex or concave to increase the cavitation effect as well. 
         [0091]    In the present embodiment, ozone from the ozonizer  5  can be inserted into the ballast water flowing in the pipe  3  before or after it passes through the jet generating device  26 . Therefore, the jet generating device  26  may be installed between the pump  3  and the static mixer  4  in the pipe  3 . 
         [0092]    While the present invention has been described based on the embodiment applicable to the removal of ozone remaining in the ballast water as aforementioned, the present invention is applicable to any water containing residual ozone. 
         [0093]    It may be emphasized that the above-described embodiments, particularly any “preferred” embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present disclosure and protected by the following claims.