WO2007032577A1

WO2007032577A1 - Electrolytic sterilizing apparatus for ship ballast water

Info

Publication number: WO2007032577A1
Application number: PCT/KR2006/000116
Authority: WO
Inventors: Eun-Chan Kim; Kyoung-Soon Shin; Kook-Jin Kang; Kang-Pyung Lee; Young-Joon Kim
Original assignee: Korea Ocean Research And Development Institute
Priority date: 2005-09-14
Filing date: 2006-01-11
Publication date: 2007-03-22
Also published as: US20080277274A1; JP4723647B2; EP1945575A1; CN101331087B; JP2009507638A; EP1945575A4; CN101331087A; KR100597254B1

Abstract

An electrolytic sterilizing apparatus comprises an electrolytic module (10) including an inlet port (11-1) disposed at one end thereof for allowing ballast water (40) to be introduced therethrough, an outlet port (11-2) disposed at the other end thereof for allowing the ballast water (40) to be discharged therethrough, a baffle unit (20) mounted at the inlet port (11-1) side for generating eddy flow, a sensor (30) mounted at the outlet port (11-2) side for measuring residual chlorine concentration, and a chamber (11) disposed between the baffle unit (20) and the sensor (30), the chamber (11) having electrode sets (12-1) mounted therein, each of the electrode sets (12-1) including a pair of electrodes (12), a power supply unit (50) for supplying power to the electrolytic module (10), and a connecting unit (60) including a pump (61) for introducing and discharging the ballast water (40), a pipe (62) connected to the pump (61), and a valve (63).

Description

ELECTROLYTIC STERILIZING APPARATUS FOR SHIP

BALLAST WATER

Technical Field

[1] The present invention relates to an electrolytic sterilizing apparatus for ship ballast water, and, more particularly, to an electrolytic sterilizing apparatus for ship ballast water wherein an electrolytic module having plate-shaped or mesh-shaped electrode sets mounted therein is connected to a pipe, through which ballast water flows, the ballast water is sterilized by an electrochemical reaction generated when the ballast water comes into contact with the surfaces of the electrodes disposed in the electrolytic module while the ballast water passes through the electrolytic module, the amount of input power is automatically adjusted by a residual chlorine concentration measuring sensor to constantly maintain the concentration of residual chlorine contained in the discharged ballast water.

Background Art

[2] Generally, most cargo ships, which are used for marine transportation, transport cargo only one way, excluding round-voyage cargo ships, which are used to transport cargo in both direction of a voyage. When a cargo ship is to return after completing a fully loaded one-way voyage, it is necessary to introduce ballast water (fresh water or seawater) into the cargo ship, such that the cargo ship can be sailed in ballast. In this case, the balance, the safety, and the operation efficiency of the cargo ship are improved.

[3] However, the ballast water contains aquatic organisms, which are the principal cause of ocean ecosystem destruction, and bacilli, which are the cause of waterborne diseases. That is, the ballast water is the cause of sea contamination all over the world. For this reason, regulations on the treatment of the ballast water are prepared by International Maritime Organization (IMO).

[4] Studies on ballast water treating methods and apparatuses have been rapidly carried out in several countries, for example, in America, Europe, and Asia. The ballast water treating methods include a filtering method, an ultraviolet sterilizing method, and a high-temperature heating method. In other words, physical, chemical, and electrical treating methods and apparatuses have been developed.

[5] The electrical treating method and apparatus includes a method and apparatus for sterilizing toxic bacilli using various radicals and oxidation reduction potential generated during electrolysis. An example of such electrical treating method and apparatus is disclosed in Korean Patent Application No. 10-1995-36079 (filed on October 19, 1995) entitled 'a sterilizing apparatus for water purifiers.' This sterilizing apparatus is an apparatus that sterilizes bacilli propagating in a water tank of a reverse osmosis type water purifier using radicals electrochemically generated in the water. Another example of such electrical treating method and apparatus is disclosed in Korean Patent Application No. 10-2001-7012714 (filed on October 5, 2001) entitled 'an electrolytic sterilizing method and apparatus for water,' which is an electrolytic sterilizing method and apparatus that is capable of sterilizing raw-material cleaning water used when food is manufactured, cleaning water used to remove bacilli from instruments or containers, and drinking water of ships for a short period of time using water containing either hypochlorite and silver ions or hypochlorite, silver ions, and copper ions. Yet another example of such electrical treating method and apparatus is disclosed in Korean Patent Application No. 10-2002-36086 (filed in the name of the inventor of the present application on June 26, 2002) entitled 'electrolytic sterilizing equipment for discharged water in a sewage treatment plant,' which sterilizes the discharged water in the sewage treatment plant by electrolysis.

[6] The above-described conventional arts are characterized in that the hypochlorite contained in the electrolyzed water is introduced into water to be sterilized, whereby the water is sterilized. Specifically, the water to be sterilized and the sterilizing water are divided from each other, and the hypochlorite and the radicals contained in the sterilizing water, which has been electrolyzed, are introduced into the water to be sterilized. However, the lives of the radicals generated during the electrolysis are very short (for example, 1/100 seconds or less for hydroxyl radical). As a result, the radicals decompose before the radicals reach the water to be sterilized. Furthermore, the water is sterilized by primarily the hypochlorite ions, which have a relatively long life span, while the sterilization effect by the oxidation reduction potential generated adjacent to the surfaces of the electrodes is not utilized. Consequently, the sterilization efficiency is very low. Especially for the ballast water, the amount of which is huge, and therefore, instantaneous sterilization is necessary, a solution for the above-mentioned problems is desperately needed. Also, when the concentration of residual chlorine inevitably generated during electrolysis exceeds a predetermined level, the residual chlorine has a harmful effect on ocean ecosystem. Consequently, a proper solution to the above-mentioned problem is urgently required. Disclosure of Invention

Technical Problem

[7] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an electrolytic sterilizing apparatus for ship ballast water that is capable of enabling ballast water to directly pass through an electrolytic module, such that the ballast water comes into direct contact with the surface of electrodes, at which radicals and oxidation reduction potential are generated, and therefore, the ballast water is sterilized to the extent that the ballast water satisfies the discharge criterion of the ballast water, and effectively inactivating aquatic organisms, coliform bacilli, and general microorganisms remaining in the ballast water while generating a low concentration of residual chlorine.

Technical Solution

[8] In accordance with the present invention, the above and other objects can be accomplished by the provision of an electrolytic sterilizing apparatus for eliminating or inactivating aquatic organisms remaining in ship ballast water, such as bacilli, wherein the electrolytic sterilizing apparatus comprises: an electrolytic module including an inlet port disposed at one end thereof for allowing ballast water to be introduced therethrough, an outlet port disposed at the other end thereof for allowing the ballast water to be discharged therethrough, a baffle unit mounted at the inlet port side for generating eddy flow, a sensor mounted at the outlet port side for measuring residual chlorine concentration, and a chamber disposed between the baffle unit and the sensor, the chamber having a plurality of electrode sets mounted therein, each of the electrode sets including a pair of electrodes; a power supply unit for supplying power to the electrolytic module; and a connecting unit including a pump for introducing and discharging the ballast water, a pipe connected to the pump, and a valve.

Advantageous Effects

[9] According to the present invention with the above-stated construction, the electrolytic sterilizing apparatus for ship ballast water has the effect of effectively sterilizing aquatic organisms remaining in the ballast water, such as toxic vibrio cholera, coliform bacilli, and general microorganisms.

[10] Furthermore, the electrolytic sterilizing apparatus for ship ballast water according to the present invention can be operated at low voltage, for example, 20V or less, and therefore, there is no possibility of electric shock. Also, the amount of residual chlorine can be automatically adjusted. Consequently, the electrolytic sterilizing apparatus for ship ballast water according to the present invention has the effect of treating the ballast water such that the ballast water satisfies the discharge criterion of the ballast water. In addition, the automatic polarity switching mode is adopted in the electrolytic sterilizing apparatus for ship ballast water according to the present invention, and therefore, scale is easily removed from the electrodes. Consequently, the electrolytic sterilizing apparatus for ship ballast water according to the present invention has the effect of preventing the scale from accumulating on the electrodes, and therefore, maintaining the sterilization efficiency for a long period of time. Description of Drawings

[11] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[12] FlG. 1 is a view illustrating a sterilizing principle of an electrolytic sterilizing apparatus according to the present invention;

[13] FlG. 2 is a concept view illustrating an electrolytic sterilizing apparatus for ship ballast water according to the present invention;

[14] FIGS. 3 A and 3B are a plan view and a perspective view respectively illustrating parallel type electrode sets according an embodiment of the present invention;

[15] FlG. 4 is an enlarged view of the electrolytic module shown in FlG. 2;

[16] FlG. 5 is a vertical sectional view taken along line A-A' of FlG. 2;

[17] FlG. 6 is a detailed view of the electrode sets shown in FlG. 4;

[18] FIGS. 7 A and 7B are plan views respectively illustrating a mesh-shaped electrode and a plate-shaped electrode according to the present invention;

[19] FlG. 8 is a perspective view, in section, illustrating a baffle unit according to the present invention; and

[20] FIGS. 9 A and 9B are graphs respectively illustrating the total amount of chlorine generated according to input power and the amount of b ioconcentration (chlorophyll) changed according to input power in the electrolytic sterilizing apparatus according to the present invention.

Mode for Invention

[21] Now, an electrolytic sterilizing apparatus for ship ballast water according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[22] FlG. 1 is a view illustrating a sterilizing principle of an electrolytic sterilizing apparatus according to the present invention, FlG. 2 is a concept view illustrating an electrolytic sterilizing apparatus for ship ballast water according to the present invention, FIGS. 3 A and 3B are a plan view and a perspective view respectively illustrating parallel type electrode sets according an embodiment of the present invention, FlG. 4 is an enlarged view of the electrolytic module shown in FlG. 2, FlG. 5 is a vertical sectional view taken along line A-A' of FlG. 2, FlG. 6 is a detailed view of the electrode sets shown in FlG. 4, FIGS. 7 A and 7B are plan views respectively illustrating a mesh-shaped electrode and a plate-shaped electrode according to the present invention, FlG. 8 is a perspective view, in section, illustrating a baffle unit according to the present invention, and FIGS. 9 A and 9B are graphs respectively illustrating the total amount of chlorine generated according to input power and the amount of b ioconcentration (chlorophyll) changed according to input power in the electrolytic sterilizing apparatus according to the present invention.

[23] Referring first to FlG. 1, the sterilizing principle of the electrolytic sterilizing apparatus according to the present invention is illustrated. Specifically, instantaneous sterilization is accomplished by oxidation reduction potential (ORP) and radicals generated at the surfaces of electrodes 12, and sterilization reaction is maintained by generated residual chlorine (hypochlorite). When water is electrolyzed, radicals, such as hydroxyl radical (OH-), hydroperoxyl radical (HOO-), superoxide radical (O -), hydrogen peroxide (H O ), and hypochlorite ion (OCl-), are generated. The radicals are characterized that the radicals have high oxidation reduction potential (2V), and the radicals uniformly react with almost all the organic matter at very high speed.

[24] Consequently, when the water passes through the electrodes 12 of the electrode sets according to the present invention, most aquatic organisms, coliform bacilli, and general microorganisms remaining in the water are instantaneously sterilized (exterminated) by the oxidation reduction potential and radicals. Some surviving organisms are inactivated by the residual chlorine. The mechanism for sterilizing ballast water by the electrolytic module will be described in detail below.

[25] (1) Sterilization by radicals

[26] When water is electrolyzed, radicals, such as hydroxyl radical (OH-), hydroperoxyl radical (HOO-), superoxide radical (O -), and hydrogen peroxide (H O ), mainly generated at the anode. The radicals are characterized in that the radicals can instantaneously sterilize bacilli by ion exchange even though the radicals are unstable and exist for a very short period of time, for example, from a few seconds to one-several hundred millionths of a second.

[27] For example, the hydrogen peroxide, which is generated by the reaction: 2OH -> H

O , is a strong oxidizing agent that effectively decomposes pollutants by oxidation, and the hydroxyl radical ion (OH -), which is generated at the anode and the cathode, serves to eliminate pollutants by an oxidation-reduction reaction.

[28] (2) Instantaneous sterilization by oxidation reduction potential

[29] When direct current voltage is applied to water, oxidation reduction potential is generated. At this time, when + oxidation reduction potential generated at the anode (+) is 1100 mV or more, the cell membranes of coliform bacilli and other bacilli are ruptured, and then microorganisms, such as bacilli, are instantaneously sterilized.

[30] Specifically, when the microorganisms are in an electric field, minute pores are formed at the cell membranes of the microorganisms. External electrolytic water is introduced into the microorganisms through the minute pores by an osmotic action, and therefore, the cells are inflated. When the inflated cells reach the critical point, the cell membranes are ruptured by hemolysis, and therefore, the cells are exterminated. This process is completed within a very short period of time, for example, 10^" seconds. Consequently, instantaneous sterilization is accomplished.

[31] At this time, it is possible to maximize the sterilization effect due to the oxidation reduction potential by periodically switching the polarities (the positive pole and the negative pole). Specifically, the oxidation reduction potential between the positive pole and the negative pole is further increased by switching the polarities, and therefore, the sterilization effect is also improved. Especially when the electrode polarity switching cycle is reduced within a unit of seconds, i n consideration of the high flow speed in a ballast water pipe, through which ballast water introduced into the electrolytic sterilizing apparatus flows, the sterilization effect is further improved.

[32] (3) Continuous sterilization by generated residual chlorine

[33] When seawater is electrolyzed, some of salt (NaCl) in the seawater is converted into residual chlorine (OCl-, HOCl). The hypochlorite is a kind of radical, however, the hypochlorite has a life span longer than other radicals, and therefore, microorganisms are more effectively sterilized by the hypochlorite. The concentration of the residual chlorine generated during electrolysis of the seawater is related to coating materials of the electrode, exposure time, and the amount of input power. When water having high concentration of residual chlorine is discharged into the sea, the high concentration of residual chlorine may destroy aquatic organisms. Consequently, it is necessary to keep the concentration of residual chlorine as low as possible. The main concept of the present invention is to performing a sterilizing process for a short period of contact time with a low electrical current using electrodes that can reduce the amount of hypochlorite generated.

[34] FIG. 2 is a concept view illustrating an electrolytic sterilizing apparatus 100 for ship ballast water according to the present invention. When a tank of a ship is to be filled with ballast water, two inlet valves, i.e., an external inlet valve 63-1 and a tank inlet valve 63-3, are opened, and two outlet valves, i.e., a tank outlet valve 63-2 and an external outlet valve 63-4, are closed such that seawater is introduced into the tank of the ship through the external inlet valve 63-1 by a pump 61, and the seawater is directly sterilized in an electrolytic module 10 by electrolysis. When the ballast water sterilized by the electrolysis is to be discharged out of the tank of the ship, the above- described process is performed in reverse. A connecting unit 60 of the electrolytic sterilizing apparatus 100 according to the present invention may have a filter (not shown) for eliminating floating solid matter, which is disposed at the inlet side of the external inlet valve 63-1. At the front end of the conventional ballast pump is generally mounted a strainer (filtering unit) for preventing introduction of the floating solid matter. Consequently, the floating solid matter contained in the introduced water, which has not been yet sterilized by electrolysis, is eliminated by the strainer, and therefore, it is possible to construct the electrolytic sterilizing apparatus according to the present invention such that the floating solid matter is eliminated by the strainer without the provision of the additional filter.

[35] The electrolytic module 10 according to the present invention has a plurality of electrode sets 12-1 mounted in a chamber 11, i.e., a main body of the electrolytic module 10, which is disposed in the middle of the electrolytic module 10. Each of the electrode sets 12-1 includes positive electrodes 12-4 and negative electrode 12-5. At opposite ends of the chamber 11 are disposed an inlet port 11-1 and an outlet port 11-2, which are connected to a pipe 62 for allowing the ballast water to flow therethrough. On the pipe 62 disposed outside the inlet port 11-1 and the outlet port 11-2 are mounted a plurality of inlet and outlet valves 63-1, 63-2, 63-3, and 63-4. At the inlet port 11-1 side of the electrolytic module 10 is mounted a baffle unit 20 for generating eddy flow. At the outlet port 11-2 side of the electrolytic module 10 is mounted a sensor 30 for measuring residual chlorine concentration. When power from a power supply unit 50 is supplied to the electrolytic module 10, the electrolytic module 10 electrolyzes the ballast water 40, by enabling the ballast water to pass between the electrode sets 12-1, such that the ballast water 40 can be treated by an electrochemical reaction. Here, the pump 61, the pipe 62, and the valves 63 together constitute the connecting unit 60.

[36] The baffle unit 20, which is mounted at the inlet port 11-1 side of the electrolytic module 10, serves to drive the introduced water, which has not been yet sterilized by electrolysis, such that eddy flow can be generated in the introduced water. The residual chlorine concentration measuring sensor 30, which is mounted at the outlet port 11-2 side of the electrolytic module 10, is a control unit for controlling the amount of residual chlorine in the ballast water 40 electrolyzed while passing through the electrolytic module 10 within a predetermined range. Specifically, the residual chlorine concentration measuring sensor 30 sends a signal to the power supply unit 50 to control the electrical current of the electrode sets 12-1 mounted in the electrolytic module 10 to be increased or decreased. This uses a fact that the amount of residual chlorine in the electrolyzed water is generated in proportion to the amount of current.

[37] Also, it is necessary that the chamber 11 of the electrolytic module 10 be made of a material having high strength to endure high water pressure of the ballast pump, high oxidation resistance to endure oxidizing matter, such as salt in the seawater and radicals generated during electrolysis, and high nonconductivity to prevent current flow.

[38] The power supply unit 50 adopts a polarity switching mode, in which the polarities of the electrodes 12, i.e., the positive pole and the negative pole, are periodically switched to effectively clean the electrodes 12. In other words, the polarity switching mode is a kind of automatic cleaning mode for removing scales from the electrodes 12. The effect of sterilization by oxidation reduction potential is further improved by periodically switching the polarities of the electrodes 12 as described above. Consequently, the effect of sterilization by oxidation reduction potential is improved in the electrolytic sterilizing apparatus 100 for sterilizing the ballast water 40. Preferably, the power supply unit 50 converts alternating current power into direct current power, periodically switches the polarities of the electrodes 12 using a built-in timer (not shown), and supplies power having low direct current voltage, for example, 20 V or less, to the electrodes 12 in the electrolytic module 10.

[39] The switching cycle may be somewhat extended when the electrode sets are disposed perpendicular to the flow direction of ballast water. However, the flow speed of the ballast water reaches approximately 100 to 300 cm/sec when the electrode sets are disposed in parallel with the flow direction of ballast water, and therefore, the exposure time is only a second or less. Consequently, it is more preferable to select a power supply unit 50 having a short switching cycle, for example, a switching cycle within a unit of seconds.

[40] Alternatively, another switching mode for switching the polarities of the electrodes while the power is supplied may be considered. For example, the direct current power is converted into the alternating current power, a cycle of the alternating current is adjusted by a frequency inverting unit (inverter), and voltage of the alternating current power is lowered to 20 V or less such that power having low alternating current voltage, for example, 20 V or less, to the electrodes 12, whereby the sterilization efficiency is improved. When the voltage of the alternating current power is lowered without passing through a rectifier, and the lowered voltage is supplied to the electrodes, since the alternating current power is a power having a cycle, the polarities of the electrodes can be periodically switched in a natural manner. Consequently, the alternating current power has higher efficiency than the direct current power. However, the alternating current has a problem in that the alternating current shows a gentle curve unlike the alternating current, and therefore, the service lives of the electrodes are somewhat reduced.

[41] FIGS. 3 A and 3B are a plan view and a perspective view schematically illustrating parallel type electrode sets according an embodiment of the present invention. Especially, FIG. 3 A illustrates the structure of the electrode sets 12-1 according to the present invention mounted in the chamber 11. Specifically, the electrode sets 12-1 are arranged in parallel with the flow direction of the ballast water 40 while the electrode sets 12-1 are divided into two groups.

[42] The present invention is characterized in that the electrodes 12 of the electrolytic module are arranged in parallel with the flow direction of the ballast water 40, and the area of each electrode 12, the number of the electrodes 12, and the number of the electrode groups are varied based on the amount of ballast water 40 discharged by the pump to control the amount of current. The electrodes may be arranged either perpendicular to or in parallel with the flow direction of the ballast water. The perpendicular type electrode sets have higher instantaneous sterilization efficiency than the parallel type electrode sets. However, the electrodes 12 of the perpendicular type electrode sets interrupt the flow of ballast water, and therefore, the durability of the electrodes 12 may be deteriorated. Consequently, it is more preferable to arrange the electrodes 12 in parallel with the flow direction of the ballast water.

[43] In the parallel type electrode sets, however, the contact time between the ballast water 40 and the electrodes 12 is low, and therefore, the instantaneous sterilization efficiency may be reduced. For this reason, as shown in FIG. 2, the baffle unit 20 for generating eddy flow is mounted at the inlet port 11-1 side such that the eddy flow is generated in the ballast water 40, and therefore, the contact time between the ballast water 40 and the electrodes 12 is maximized. Furthermore, as occasion demands, mesh-shaped electrodes 12-3 rather than plate-shaped electrodes 12-2 are used as the electrodes 12, whereby the instantaneous sterilization efficiency is increased for the same amount of current (see FIGS. 7A and 7B).

[44] FIG. 4 is an enlarged view of the electrolytic module shown in FIG. 2, FIG. 5 is a vertical sectional view taken along line A-A' of FIG. 2, and FIG. 6 is a detailed view of the electrode sets shown in FIG. 4. Specifically, FIG. 4 is a sectional view of the electrolytic module 10 cut at right angles to the electrode arrangement direction. As shown in FIGs. 4 and 6, the electrode sets 12-1 are divided into several groups. Each of the electrode sets 12-1 has a positive power source 50-1 and a negative power source 50-2. The electrode sets 12-1 are arranged such that the positive power source 50-1 of one of the electrode sets 12-1 is adjacent to the positive power source 50-1 of a neighboring electrode set 12-1, and the negative power source 50-2 of one of the electrode sets 12-1 is adjacent to the negative power source 50-2 of another neighboring electrode set 12-1. The electrode sets 12-1 are constructed such that the negative electrodes 12-5 and the positive electrodes 12-4 are alternately arranged, and the negative electrodes 12-5 of one of the electrode sets 12-1 correspond to the positive electrodes 12-4 of the neighboring electrode set 12-1 while the positive electrodes 12-4 of one of the electrode sets 12-1 correspond to the negative electrodes 12-5 of the neighboring electrode set 12-1. When the distance between the electrodes 12 is too small, the flow of the ballast water is interrupted. When the distance between the electrodes 12 is too large, on the other hand, the electrolysis efficiency is reduced. According to the present invention, the distance between the electrodes 12 is set to approximately 5 to 20 mm to effectively prevent the interruption of the flow of the ballast water and the reduction of the electrolysis efficiency.

[45] FlG. 5 is a sectional view of the electrolytic module 10 cut in parallel with the electrode arrangement direction. As shown in FlG. 5, the mesh-shaped electrodes 12-3 are arranged side by side.

[46] It is necessary that the electrodes be made of conductive material having high oxidation resistance to endure oxidizing matter generated during the electrolysis and high insolubility, which is necessary for maintaining stability. Consequently, it is preferable that insoluble electrodes formed by coating titanium with iridium oxide be used as the electrodes according to the present invention.

[47] In order to maintain the distance between the electrodes 12 of the electrode sets

12-1 and prevent short circuits in the electrolytic module 10, the electrode sets 12-1 may be mounted in a spacer or an inner case. It is necessary that the spacer or the inner case be insulated. Consequently, it is preferable that the spacer or the inner case be made of a polyvinyl chloride (PVC)-based insulating synthetic resin. More preferably, the spacer or the inner case is made of a material having high resistance against oxidizing matter generated during the electrolysis, such as poly propylene (PP) or fiberglass reinforced plastic (FRP).

[48] FIGS. 7 A and 7B are plan views respectively illustrating the mesh-shaped electrode and the plate-shaped electrode according to the present invention. The mesh- shaped electrode and the plate-shaped electrode are used in the electrolytic sterilizing apparatus according to the present invention. The mesh-shaped electrode 12-3, which is shown in FlG. 7A, is used for both the perpendicular type electrode sets and the parallel type electrode sets. On the other hand, the plate-shaped electrode 12-2, which is shown in FlG. 7B, is used for only the parallel type electrode sets.

[49] As previously described in connection with FlG. 3, the electrodes 12 are arrangement either perpendicular to or in parallel with the introduction direction of ballast water 40. In the case of the perpendicular arrangement, the ballast water must pass through the surfaces of the electrodes. Consequently, the mesh-shaped electrode 12-3 is used for the perpendicular arrangement. In the case of the parallel arrangement, the ballast water passes between the surfaces of the electrodes. Consequently, not only the mesh-shaped electrode 12-3 but also the plate-shaped electrode 12-2 is used for the perpendicular arrangement. If necessary, the mesh-shaped electrode 12-3 and the plate- shaped electrode 12-2 may be used together in the electrolytic module.

[50] In the case of the parallel arrangement, however, it is preferable to use the mesh- shaped electrode, which generates relatively more eddy flow to increase contact time between the ballast water and the electrode surfaces when the ballast water passes between the electrode surfaces. Consequently, the sterilization efficiency is increased when the mesh-shaped electrode is used. On the other hand, the mesh-shaped electrode does not endure impacts as compared with the plate-shaped electrode. For this reason, when the mesh-shaped electrode is subject to strong water pressure for a long period of time, the mesh-shaped electrode may be physically damaged, and therefore, the service life of the mesh-shaped electrode is shorter than that of the plate-shaped electrode. Consequently, the electrodes 12 of the first-group electrode set, which comes into first contact with the introduced ballast water 40, is formed of the plate-shaped electrodes 12-2 such that damage to or wear of the electrodes due to the pressure caused when the ballast water is introduced is minimized, and the other-group electrode sets 12-1 are formed of the mesh-shaped electrodes 12-3 such that the contact time between the electrodes and the ballast water is maximized by the eddy flow generated at the electrode surfaces.

[51] FIG. 8 is a perspective view, in section, illustrating the baffle unit 20 for generating eddy flow. As shown in FIG. 8, the introduced ballast water is whirled by baffle blades 20-1 attached to the inner wall of the baffle unit 20 on the slant. Consequently, the contact time between the ballast water and the electrode surfaces is increased, and therefore, the sterilization efficiency is improved.

[52] As described above, the electrolytic sterilizing apparatus according to the present invention sterilizes the ballast water using the electrolytic module, in which multi- group electrode sets are mounted. The ballast water is introduced into the electrolytic module from the outside by the ballast pump. When the introduced ballast water passes through the electrode sets, which are arranged in parallel with the flow direction of the ballast water, the ballast water comes into contact with the electrode surfaces, and therefore, the ballast water is directly sterilized by the electrochemical reaction.

[53] Up until now, the amount of residual chlorine is not particularly restricted.

Generally, discharged ballast water is approved by International Maritime Organization (IMO) when the amount of residual chlorine in the discharged ballast water is below approximately 20 ppm. Consequently, it is preferable to reduce the concentration of chlorine contained in the discharged ballast water below approximately 20 ppm. The residual chlorine measuring sensor and the power supply unit are automatically operated to adjust the concentration of residual chlorine contained in the ballast water such that the concentration of residual chlorine can be maintained below the predetermined level.

[54] The ballast water is electrolyzed according to the above-described process, and the ballast water having the adjusted concentration of residual chlorine is discharged out of the electrolytic sterilizing apparatus through the outlet port of the electrolytic module and the pipe.

[55] According to the present invention, the residual chlorine concentration based on input power used in the electrolytic sterilizing apparatus and the bioconcentration, which is measured by chlorophyll, based on input power used in the electrolytic sterilizing apparatus were measured to confirm the sterilizing power of the electrolytic sterilizing apparatus. FIGS. 9 A and 9B are graphs respectively illustrating the total amount of chlorine generated according to the input power and the amount of b iocon- centration, which is measured by chlorophyll, based on the input power.

[56] Table 1 [57]

[58] As can be seen from Table 1 and FIGS. 9 A and 9B, the chlorine concentration (total amount of chlorine generated) increased as the input power was increased. When the input power was 30 W, 22 mg/1 of chlorine concentration was generated, and therefore, the discharged ballast water met the recommended criterion of chlorine concentration. Furthermore, approximately 99 % of the bioconcentration was exterminated as compared to original water, and therefore, the sterilization efficiency was satisfied.

[59] It is understood from the above experiment results that the amount of residual chlorine and the sterilization efficiency of the ballast water are adjusted by controlling the input power, and therefore, more efficient sterilization is accomplished.

[60] Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[1] An electrolytic sterilizing apparatus (100) for eliminating or inactivating aquatic organisms remaining in ship ballast water, such as bacilli, wherein the electrolytic sterilizing apparatus comprises: an electrolytic module (10) including an inlet port (11-1) disposed at one end thereof for allowing ballast water (40) to be introduced therethrough, an outlet port (11-2) disposed at the other end thereof for allowing the ballast water (40) to be discharged therethrough, a baffle unit (20) mounted at the inlet port (11-1) side for generating eddy flow, a sensor (30) mounted at the outlet port (11-2) side for measuring residual chlorine concentration, and a chamber (11) disposed between the baffle unit (20) and the sensor (30), the chamber (11) having a plurality of electrode sets (12-1) mounted therein, each of the electrode sets (12-1) including a pair of electrodes (12); a power supply unit (50) for supplying power to the electrolytic module (10); and a connecting unit (60) including a pump (61) for introducing and discharging the ballast water (40), a pipe (62) connected to the pump (61), and a valve (63).

[2] The apparatus as set forth in claim 1, wherein the chamber (11) is an oxidation- resistance nonconductive member.

[3] The apparatus as set forth in claim 1, wherein the electrodes (12) include plate- shaped electrodes (12-2).

[4] The apparatus as set forth in claim 1, wherein the electrodes (12) include mesh- shaped electrodes (12-3).

[5] The apparatus as set forth in claim 1, wherein the electrodes (12) are manufactured by coating titanium with iridium oxide.

[6] The apparatus as set forth in claim 1, wherein the electrodes (12) are arranged at an interval of approximately 5 to 20 mm.

[7] The apparatus as set forth in claim 1, wherein the electrode sets (12-1) are disposed in parallel with the flow direction of the ballast water (40) such that the amount of current can be adjusted according to the flow speed and the flow rate of the ballast water (40).

[8] The apparatus as set forth in claim 1, 3 or 4, wherein the electrodes (12) of the first-group electrode set, which comes into first contact with t he introduced ballast water (40), is formed of the plate-shaped electrodes (12-2), and the other- group electrode sets (12-1) are formed of the mesh-shaped electrodes (12-3).

[9] The apparatus as set forth in claim 1, 3 or 7, wherein the plate-shaped electrodes

(12-2) are used only when the electrode sets (12-1) are disposed in parallel with the flow direction of the ballast water (40).

[10] The apparatus as set forth in claim 1, wherein the electrode sets (12-1) are disposed perpendicular to the flow direction of the ballast water (40) such that the amount of current can be adjusted according to the flow speed and the flow rate of the ballast water (40).

[11] The apparatus as set forth in claim 1, wherein the electrode sets (12-1) are arranged such that a positive power source (50-1) of one of the electrode sets (12-1) is adjacent to a positive power source (50-1) of a neighboring electrode set (12-1), and a negative power source (50-2) of one of the electrode sets (12-1) is adjacent to a negative power source (50-2) of another neighboring electrode set (12-1), and the electrode sets (12-1) are constructed such that negative electrodes (12-5) and positive electrodes (12-4) are alternately arranged, and the negative electrodes (12-5) of one of the electrode sets (12-1) correspond to the positive electrodes (12-4) of the neighboring electrode set (12-1) while the positive electrodes (12-4) of one of the electrode sets (12-1) correspond to the negative electrodes (12-5) of the neighboring electrode set (12-1).

[12] The apparatus as set forth in claim 1, wherein the power supply unit (50) converts alternating current power into direct current power, periodically switches the polarities of the electrodes (12) using a timer, and supplies power having low direct current voltage, 20 V or less, to the electrodes (12).

[13] The apparatus as set forth in claim 1, wherein the power supply unit (50) converts direct current power into alternating current power, adjusts a cycle of the direct current using a frequency inverting unit, and supplies power having low alternating current voltage, 20 V or less, to the electrodes (12).

[14] The apparatus as set forth in claim 1, 12 or 13, wherein the amount of current supplied from the power supply unit (50) to the electrolytic module (10) is controlled by the residual chlorine concentration measuring sensor (30).