Method and system for applying superimposed time-varying frequency electromagnetic wave for marine ballast water bio-fouling control

Abstract

The disclosure relates to a method and system for treating ballast water and ballast water treatment systems in order for treatment effects to be carried out, such as controlling the transportation of undesirable and invasive marine organisms. In particular, the disclosure relates to methods and systems for applying a superimposed time-varying frequency electromagnetic wave comprising both AC and DC components in a pulsating manner to ballast water within a ballast water treatment system.

Claims

1. A method of treating ballast water containing aquatic organisms, comprising applying a superimposed time-varying frequency AC electromagnetic wave to the ballast water, the method comprising the steps of: generating the superimposed time-varying frequency AC electromagnetic wave in which an AC driving signal with time-varying frequency is riding on a DC output with a predefined DC bias voltage to form a net superimposed DC biased time-varying pulsating AC electromagnetic wave; transmitting the net superimposed DC biased time-varying pulsating AC electromagnetic wave to one or more emitters, the emitters being configured to transmit the net superimposed DC biased time-varying pulsating AC electromagnetic wave, and subjecting the ballast water to the net superimposed DC biased time-varying pulsating AC electromagnetic wave so as to excite the ballast water and the aquatic organisms therein, wherein the excitation causes a flow of ionic current having a DC component travelling in a pulsating and time-varying AC manner in the ballast water and resident aquatic organisms which induces a vibration of electrons and molecules therein that acts to kill the said aquatic organisms to prevent biofouling.

2. The method of claim 1 wherein the method includes the steps of: supplying rectified DC power to an ultra-low frequency (ULF) wave generator, generating an alternating time-varying modulated low frequency pulsating wave from the rectified DC power, and superimposing the alternating time-varying modulated low frequency pulsating wave to form the net superimposed DC biased time-varying pulsating AC electromagnetic wave.

3. The method as claimed in claim 1, comprising the further step of passing the ballast water through a mechanical filtration process or UV unit prior to treatment by the net superimposed DC biased time-varying pulsating AC electromagnetic wave.

4. The method as claimed in claim 1, wherein the emitters are contained in a housing and the ballast water is passed through the housing.

5. The method as claimed in claim 4, wherein the housing is a metallic or conductive material and one emitter is provided in the ballast water and a further emitter is provided on the housing.

6. The method as claimed in claim 4, wherein the housing is a non-metallic or non-conductive material and at least one pair of emitters is provided in the ballast water.

7. The method as claimed in claim 1, wherein the frequency of the superimposed time-varying frequency electromagnetic wave is between about 100 Hz and about 1 MHz.

8. The method as claimed in claim 7, wherein the frequency of the superimposed time-varying frequency AC electromagnetic wave is between about 0.1 KHz and about 200 KHz.

9. The method as claimed in claim 1, wherein the superimposed time-varying frequency AC electromagnetic wave has a sweeping frequency between about 1 Hz and about 1 KHz.

10. The method as claimed in claim 9, wherein the superimposed time-varying frequency AC electromagnetic wave has a sweeping frequency between about 10 Hz and about 500 Hz.

11. The method as claimed in claim 1, wherein the generated net superimposed DC biased time-varying pulsating AC electromagnetic wave is a DC biased alternating current having fixed frequency, time-varying frequency or random.

12. The method as claimed in claim 1, wherein at least one emitter comprises a steel rod coated with MgO+MgCO.sub.3 or other alkali material to create an alkaline environment and the net superimposed DC biased time-varying pulsating AC electromagnetic wave enables a magnetite layer to form on the steel rod.

13. The method as claimed in claim 1, wherein the net superimposed DC biased time-varying pulsating AC electromagnetic wave output current is controlled by use of an inductor coil.

14. The method as claimed in claim 1, wherein the net superimposed DC biased time-varying pulsating AC electromagnetic wave output current is controlled by a pulse width modulator.

15. A ballast water treatment system comprising: a power supply for supplying power to an alternating time-varying modulated low frequency pulsating wave generator, a device for generating a superimposed time-varying frequency AC electromagnetic wave and having at least two output terminals, the device comprising an alternating current (AC) wave generator for generating an AC driving signal of AC electromagnetic wave having a time-varying frequency at a desired sweeping time, and a direct current (DC) biasing unit electrically coupled in series with the AC wave generator and for producing a DC output with a predefined DC bias voltage, the DC biasing unit being configured such that the DC output is mixed with the AC driving signal to produce a superimposed DC biased time-varying pulsating AC electromagnetic wave in which the time-varying frequency AC wave is riding on the predefined DC bias voltage, and an emitter provided at one or each of a first excitation site and a second excitation site in the ballast water or in the ballast water and the ballast water treatment system and electrically coupled in series with the output terminal of the device, for transmitting the superimposed DC biased time-varying pulsating AC electromagnetic wave to ballast water containing aquatic organisms, wherein the device is electrically coupled in series with the first excitation site and the second excitation site of the ballast water or in the ballast water and the ballast water treatment system directly or through the emitter, such that the superimposed DC biased time-varying pulsating AC electromagnetic wave is applied to the ballast water or in the ballast water and the ballast water treatment system, and wherein the DC bias output and the AC driving signal are superimposed such that the superimposed DC biased time-varying pulsating AC electromagnetic wave is able to induce a flow of ionic current having a DC component travelling in a pulsating and time-varying manner in the ballast water and resident aquatic organisms or in the ballast water and resident aquatic organisms and the ballast water treatment system and effect induced vibration of electrons and molecules therein to kill the said aquatic organisms to prevent biofouling.

16. The system as claimed in claim 15, wherein the DC biasing unit is selected from the group consisting of switch mode DC power supply, an AC to DC converter, a rechargeable DC battery and an inductive diode filter.

17. The system as claimed in claim 15, wherein the DC bias voltage is selected such that the superimposed time-varying frequency AC electromagnetic wave is produced to have polar asymmetry or become a unidirectional pulsating wave.

18. The system as claimed in claim 15, wherein the frequency of the superimposed time-varying frequency AC electromagnetic wave is between about 100 Hz and about 1 MHz, and the sweeping frequency of the superimposed time-varying frequency AC electromagnetic wave is between about 1 Hz and about 1 kHz.

19. The system as claimed in claim 15, wherein both the first and second excitation sites are positioned in the ballast water in a spaced relation, or one of the first and second excitation sites is positioned on the ballast water treatment system, and the other is positioned in the ballast water.

20. The system as claimed in claim 15, wherein at least one emitter comprises a steel rod coated with MgO+MgCO.sub.3 or other alkali material to create an alkaline environment and the DC biased pulsating electromagnetic wave enables a magnetite layer to form on the steel rod.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of an exemplary arrangement of a superimposed time-varying frequency electromagnetic wave system which is constructed in accordance with a first embodiment of the invention.

(2) FIG. 2 is a schematic view of an exemplary arrangement of a superimposed time-varying frequency electromagnetic wave system which is constructed in accordance with a second embodiment of the invention.

(3) FIGS. 3A and 3B are a schematic view of an exemplary arrangement of a superimposed time-varying frequency electromagnetic wave system which is constructed in accordance with a third embodiment of the invention.

(4) FIGS. 4A and 4B are a schematic view of an exemplary arrangement of a superimposed time-varying frequency electromagnetic wave system which is constructed in accordance with a fourth embodiment of the invention.

(5) FIG. 5A to 5C are schematic views of first exemplary wave forms of the superimposed time-varying frequency electromagnetic wave.

(6) FIG. 6A to 6D are schematic views of second exemplary wave forms of the superimposed time-varying frequency electromagnetic wave.

(7) FIG. 7A to 7D are schematic views of third exemplary wave forms of the superimposed time-varying frequency electromagnetic wave.

(8) FIG. 8A to 8C are schematic views of fourth exemplary wave forms of the superimposed time-varying frequency electromagnetic wave.

(9) FIGS. 9A and 9B are schematic views of fifth exemplary wave forms of the superimposed time-varying frequency electromagnetic wave.

(10) FIG. 10 is a schematic view of an exemplary AC wave generator.

(11) FIG. 11 is a schematic view of an exemplary arrangement of a ballast water treatment system according to the invention.

(12) FIG. 12 is a schematic view of an alternative exemplary arrangement of a ballast water treatment system according to the invention.

(13) In the drawings, like parts are designated by like reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(14) While this invention is illustrated and described in relation to non-limiting preferred embodiments, the system for applying a superimposed time-varying frequency electromagnetic wave to a target object or a target region may be produced in many different configurations, sizes, forms and materials.

(15) The term medium used herein may refer to a gas, a liquid or a solid or any combination thereof, which surrounds the object, and the medium and the object form together a region that requires for desirable treatment effects. Advantageously, the medium is ionized or conductive, for example an electrolyte such as water, oil, soil and the like. In preferred embodiments of the present invention, the medium comprises ballast water.

(16) The term actuator or emitter used herein refers to an element that is able to employ the superimposed time-varying frequency electromagnetic wave to energize the target object or the target region, such that the target object or region is subjected to the treatment of the superimposed time-varying frequency electromagnetic wave.

(17) FIGS. 1 to 10 and the corresponding following description relate to methods and systems for producing a superimposed DC pulsing ionic wave current. FIGS. 11 and 12, and the corresponding description relate to the specific invention with respect to the methods and systems for treating ballast water.

(18) Referring now to the drawings, FIG. 1 provides a system 100 constructed consistent with a first embodiment of the present invention. In this embodiment of the invention, the system 100 comprises a device 110 for generating a superimposed time-varying frequency electromagnetic wave. The device 110 comprises an alternating current (AC) wave generator 112 and a direct current (DC) biasing unit 116, which is electrically coupled in series with the AC wave generator 112.

(19) The system 100 further comprises two actuators 120 each electrically coupled with a respective output terminal of the device 110.

(20) As shown in FIG. 1, the actuators 120 are immersed in a conductive liquid 130 (i.e. water, such as sea water, fresh water, estuary water) contained in a container 140. The actuator of the invention serves to energize the conductive liquid 130 with the superimposed time-varying frequency electromagnetic wave. A first excitation site 150 and a second excitation site 160 are arranged in spaced relation in the liquid, such that their connection with the actuators 120 does not cause a problem of short circuiting. The device 110, the actuators 120 and the conductive liquid 130 together form a closed loop circuit. In this embodiment, the liquid (water) 130 is to be treated for the purposes of control of bacteria and biological growth, and may include control of scale formation, control of corrosion, and/or control of water-hardness. The material of the actuators 120 can be any metals, solid conductive materials or materials coated with conductive material, and can be selected from the group consisting of steel, copper, zinc, graphite, stainless steel, titanium, metal oxide coated titanium and the like. The actuators 120 can be of any geometrical shape including round, square, rectangular and triangular shapes, and may be provided in the form of bars, rods, tubes, dishes, plates, spheres, cubes, hollow forms, solid forms, perforated forms, meshes, etc. The actuators 120 may be immersed in the liquid, or can effect a direct excitation on the conductive materials including metallic and non-metallic materials or structures.

(21) The AC wave generator 112 is electrically coupled with a power supply and configured for generating an AC driving signal of AC electromagnetic wave having a time-varying frequency at a desired sweeping time. The power supply can be a DC or AC power supply. In the preferred embodiment of the invention, the power supply is advantageously of DC nature and provides an input DC signal to the AC wave generator 112. As illustrated in FIG. 10, the AC wave generator 112 in this embodiment comprises a control unit 114 configured and programmed to generate a signal having the desired time-varying frequency at the desired sweeping time, this signal generated by the control unit 114 being in the magnitude of milli-amperes.

(22) The AC wave generator 112 further comprises one or more bridge-type circuits 115 electrically coupled to the control unit 114 to receive the signal generated by the control unit 114. The bridge-type circuit 115 is configured to be driven by the received signal to generate and amplify an AC driving signal in the magnitude range of milli-ampere to ampere, for example. This AC driving signal corresponds to the time-varying frequency AC electromagnetic wave having the desired sweeping time and is delivered to the DC biasing unit 116 for superposition on the DC output. The bridge-type circuit 115 comprises two sets of sub-circuits in parallel as illustrated. Each of the sub-circuits comprises a half-bridge driver integrated circuit in connection with two or more MOSFETs. If the main AC source is applied, an AC-to-DC converter may be embedded in the AC wave generator 112 for converting the AC power supply to a DC power supply which is then applied to the control unit 114. The power supply applies to the AC wave generator 112 a voltage according to the actual applications, for example between about 12V to about 200V.

(23) The various electronic components in the AC wave generator 112 may be provided on a printed circuit board (PCB). If an AC-to-DC converter or rectifier is needed, it may also be mounted on the PCB as a compact structure.

(24) As described above, the control unit 114 generates the time-varying frequency signal at the desired sweeping time. The sweeping time is selected to ensure the liquid has the correct time frame to expose it to the corresponding frequency for the correct exposure time period. For different applications, a wide range of frequencies may be selected. Preferably, the frequency of the superimposed time-varying frequency electromagnetic wave used in the invention may be in the range of 100 Hz to 1 MHz, preferably in the range of 100 Hz to 200 kHz, with the sweeping frequency between about 1 Hz to 1 kHz, preferably in the range of 10 Hz and 100 Hz. The waveform of the superimposed time-varying frequency electromagnetic wave can be square, triangular, rectangular, sinusoidal or other forms. In this embodiment, the control unit 114 comprises a programmable integrated circuit (IC) for time-varying the frequency of the AC driving signal, and a stabilizer circuit for stabilizing the AC driving signal.

(25) The direct current (DC) biasing unit 116 is electrically coupled in series with the AC wave generator 112 and configured for producing a DC output with a predefined DC bias voltage which may be varied or fixed. The DC biasing unit 116 is programmed such that the DC output is mixed with the amplified AC driving signal received from the AC wave generator 112 to produce the superimposed time-varying frequency electromagnetic wave where the time-varying AC wave is riding on the predefined DC bias voltage. In this embodiment, the DC biasing unit 116 is a switch mode DC power supply. A rechargeable DC battery or AC-to-DC rectifier power supply are possible alternatives for the DC biasing unit 116. When a rechargeable DC battery is used as the DC biasing unit 116, an extremely pure DC output can be generated and is particularly suitable for some applications requiring an extremely pure DC source.

(26) It is advantageous that the DC bias voltage matches the voltage and frequency of the AC pulsating wave coming from the AC wave generator 112. In general the DC bias voltage is lower than the time-varying pulsating wave voltage. The DC bias voltage is therefore adjustable to suit the different onsite treatment requirements. In some cases, the DC bias source is configured to be able to take an inflow of current/voltage if the time-varying pulsating AC wave should surge into the DC bias source.

(27) One feature of the invention is that the unique superimposed time-varying frequency electromagnetic wave can be generated only when the right combination of the AC wave generator 112, the DC biasing unit 116 and the actuators 120 are connected to one another in series.

(28) The superimposed time-varying frequency electromagnetic wave of the invention is different from the simple combination of applying a DC component and a separate time-varying frequency AC wave. If a DC component is separately applied to a time-varying frequency AC wave, there is no superimposed DC pulsed wave produced or presented in the liquid. The DC component is static and would exert separately its own DC effect, and the separate time-varying frequency AC wave, which is balanced in positive and negative amplitude without the DC characteristics, would exert its own effect too.

(29) When the input DC signal is provided to the AC wave generator 112, the generator 112 generates and amplifies an AC driving signal corresponding to the time-varying frequency AC electromagnetic wave at a specific sweeping time, which is a wave for example in sine wave form (see FIGS. 5A to 5C). The amplified AC driving signal of the time-varying frequency AC alternating electromagnetic wave is delivered to the DC biasing unit 116 where the DC bias output having a predefined a bias voltage V.sub.DC is mixed with the AC driving signal. The result of such a mix is an AC-DC superimposed signal where the time-varying AC electromagnetic wave is riding on the DC preset level to produce the superimposed time-varying frequency electromagnetic wave (hereinafter called DAC wave) having a mixed-frequency voltage. In the DAC wave, the DC component is not static but rather travels in a pulsating and time-varying manner along with the AC component. Therefore, there will be a pulsing ionic wave current containing the DC component produced in the liquid 130, i.e. there are physical ions or charges flowing in the liquid 130, which is an important and distinguishing feature of the invention. After being subject to such an ionic wave current, the internal energy including the vibrational and rotational energy of the liquid is changed, which results in the liquid molecule clusters carrying electrons or positive charge. This can change the clustering arrangement of the liquid molecule, and more importantly, the energy can be stored in the liquid for a period of time before it is completely dissipated to the surroundings. The stored energy in the liquid plays an important role for the various treatment effects.

(30) In some cases, it is necessary to control the DAC wave to have a controllable DC superimposition magnitude. For example, when the DAC wave is applied for bio-fouling control purposes, the DC biasing voltage V.sub.DC may be set such that the DC superimposition magnitude can be controlled to vary between 60 V to +60 V in continuous variations or in steps, and of course higher voltage can be applied. In general the maximum limit of the DC imposition magnitude is determined by safety operating limits and is controlled to be less than the pulsating wave peak voltage. The negative and positive polarity may be set permanently or be controlled by switching the terminal polarity at a pre-programmed frequency or manually.

(31) The polarity of the DAC wave is characterized mainly by the DC component and depends on the polarity of the DC component and the overall loop power source current flow direction. The average voltage of the DAC wave can be seen as having two components, one being the AC amplitude and the other being the DC bias voltage. Each of these magnitudes has its own function, but also they often provide a synergy effect to each other. In some scenarios, a large AC voltage amplitude is necessary, for example to deter the bio-organism attachment. In other scenarios, the DC magnitude (i.e. the DC bias voltage) is important, for example in providing sufficient current density covering the structure surfaces to be protected in corrosion control to meet the full corrosion protection criteria. Also, the ratio of AC to DC amplitudes is important in some applications such as controlling the types of disinfectant effect produced. High DC magnitude can generate more long residual time disinfectant whereas the high AC magnitude can produce more short life disinfectant. Therefore, the AC amplitude voltage and the DC bias voltage may be adjusted and selected according to the actual applications required of the DAC wave.

(32) In a preferred embodiment of the invention, the polarity of the DAC wave may be changed asymmetrically as shown in FIGS. 5A to 5C. In FIG. 5A the DAC sine wave never goes negative, in FIG. 5C the DAC sine wave never goes positive, and in FIG. 5B the DAC sine wave spends more time positive than negative. One of the methods for changing the polarity of the DAC wave is to configure the DC biasing unit to give different DC bias voltages V.sub.DC so that the polarity of the DAC sine wave may be varied, if desired.

(33) Non-sine waveforms are possible for the invention, for example square waves, rectangular waves, triangular waves or the like. FIGS. 6A to 6D and FIGS. 7A to 7D illustrate some possible variations of the waveforms. In certain applications of the DAC wave, such as when the DAC wave is applied to water in order to prevent bio-fouling, using a distorted waveform instead of a regular waveform can result in a better effect for bio-organism control. It is believed that the bio-organisms find it difficult to adapt to the changes in waveform and hence a more effective disinfection result can be realized. In FIGS. 8A to 8C, there are illustrated some examples of wave distortion. The distorted wave may be obtained by filtering diodes or filter circuits; or the AC wave generator may be programmed to produce many other possible distorted waveforms.

(34) Now turning to FIG. 2, there is illustrated a system 200 constructed consistent with a second embodiment of the present invention. The system 200 of this embodiment is structurally same as the one shown in the first embodiment above, except that an inductive diode filter 216 is selected as the DC biasing unit. The inductive diode filter 216 functions to filter all or part of the positive or negative half of the time-varying frequency AC electromagnetic wave to yield an asymmetrical wave having only positive components or negative components. In this embodiment, the DAC wave is biased to have an amplitude toward only the positive or negative direction and generate the waveforms as shown in FIGS. 9A and 9B.

(35) FIGS. 3A and 3B illustrate a system 300 constructed consistent with a third embodiment of the present invention. The system 300 of this embodiment is structurally the same as the one shown in the first embodiment above, except that the pipe 340 and the fluid such as water 330 flowing in the pipe 340 together form a target region to be treated. In FIG. 3A, the pipe 340 is made of a non-metallic material so the two actuators 320 are placed to connect with the first and second excitation sites located in the fluid. An inductor may be arranged to connect with the one of the excitation sites, if needed, to enhance the electromagnetic effect. In FIG. 3B, the pipe 340 is made of a metallic material. In this case, one actuator 320 is placed in the fluid. The other excitation site is positioned on the pipe 340 itself, and this excitation site is directly electrically coupled with the output terminal of the device for generating the DAC wave. The DAC wave can go randomly towards different directions in the liquid 330 and in the pipe 340, which ensures that many blind spots or zones in the liquid and in the pipe can be reached by the DAC wave and therefore are subject to the DAC wave treatment. In some extreme hard to reach blind spot or zone cases, an extra connection point 360 may be provided at the blind spot areas to force the return of the DAC wave.

(36) FIGS. 4A and 4B illustrate a system 400 constructed consistent with a fourth embodiment of the present invention. The system 400 of this embodiment is structurally the same as the one shown in the first embodiment described above, except that the actuators are provided in the form of a coil 420 to excite the target region. Ferrite may be incorporated within the coil or outside the coil to enhance the magnetic field effect. Likewise, the coil 420 may be immersed in the liquid (FIG. 4A) or above the liquid (4B).

(37) In the method of the invention, the actuator may be placed in the water. The location of the actuator may be a long distance from the structure such that the potential gradient created in the electrolyte is minimal. When the actuator is placed remotely from the structures or vice versa, the DAC wave will be able to distribute evenly across the entire structure surface, providing a uniform and complete protection effect.

(38) The systems discussed in the above embodiments can produce the required DAC wave uniquely. The right system can be chosen for a specific application for the desired treatment effect.

(39) The present invention provides a specific application of the time-varying DC pulsating wave described above for treatment of ballast water and ballast water treatment systems.

(40) FIGS. 11 and 12 illustrate alternative embodiments of the present invention. It should be noted that the elements shown in each embodiment are interchangeable with the elements illustrated in any other embodiment. FIG. 11 shows the effect of the system with a non-metallic housing structure or a steel (or other metal) housing with non-metallic inner lining and FIG. 12 shows the effect for a metallic housing without a non-metallic lining structure.

(41) In this invention, as shown in FIGS. 11 and 12, the time-varying DC pulsating wave disinfection system is used on ballast water 330 that is passed into the treatment system via a mechanical separation means 500. Pre-separation of particles and organisms of >50 m in a major length dimension is carried out using mechanical separation means 500 which can be any suitable means such as a strainer, cyclone or filter. It is anticipated some bio-organisms of >50 m may be able to pass through the separators 500 but the majority shall be removed in the filtering separation process. An UV unit positioned in the process flow after the separators 500 may be incorporated and will not affect the system performance. Such addition may be considered as an optional feature of the invention.

(42) The DC biased time-varying pulsating wave is generated by a DAC wave generator 110. A power supply source 501 provides power to a ULF wave generator 110, typically rectified from a 230V/440V, 50/60 Hz AC power supply. The wave generator 110 comprises a time-varying DC pulsating wave generator consisting of an electronic circuit board which converts the incoming rectified DC current into an alternating time-varying modulated low frequency wave as output. The DC superimposing can be done by a variety of means, for example by using a variable output DC switch mode power supply or rechargeable DC battery as indicated by reference 610 in FIG. 12 or an inductive diode filter as indicated by reference 510 in FIG. 11, which create a similar treatment effect to an asymmetrical DC superimposed pulsed time-varying wave but do not require any additional DC power source.

(43) FIG. 11 illustrates an arrangement for a non-conductive material housing 540, in which two emitters 520 are positioned within the housing 540 in the ballast water 330. FIG. 12 illustrates an arrangement for a metallic or conductive material housing 640, in which one emitter 620 is positioned within the housing 640 in the ballast water 330 and the other emitter 660 is positioned on the metallic housing 640 itself.

(44) The emitters 520, 620 that are placed in the ballast water preferably consist of semi- or non-consumable materials such as graphite, or may comprise, for example, a silicon chromium iron, a conductive carbon or conductive carbon coated substrate, a metal oxide coated substrate, or a platinum coated titanium or a diamond doped substrate.

(45) The corresponding emitter 520, 660 that receives the net DC pulsed time-varying wave can be made of any metallic material or conductive non-metallic material. For a metallic housing 640, the housing itself may be used as the net DC wave receiving emitter 660.

(46) The number of emitters or emitter pairs may be multiplied in series or separately depending on the treatment efficacy requirement. The frequency and strength of the emitter pairs may also be controlled separately to meet the specific frequency range requirement of different organisms.

(47) When using a non-metallic housing 540, as shown in FIG. 11, a good avalanche current can be produced concurrently. In the case of a non-metallic housing 640, as shown in FIG. 12, a non-conductive material lining may be provided (not shown) to improve the production of avalanche current. However, a metallic housing 640, of a material such as steel, will also receive a corrosion protection effect similar to cathodic protection by production of a magnetite protection layer generated by the emitter excitation energy.

(48) FIGS. 11 and 12 show inductor coils 570 to control the output current. However, alternatively, a Pulse Width Modulation technique may be incorporated in the DAC wave generator circuit design and can then be used to control the output current, output waveform design, the pulsing frequency, the frequency range, the sweeping frequency and the voltage applied.

(49) The DC biased time-varying pulsating wave generated by the DAC wave generator 110 has several important characteristics. The pulsating wave has a controllable DC superimposition magnitude which, for all practical purposes, can be controlled to vary between 60 V to +60 V in continuous variations or in steps, although higher voltages can be applied. In general the maximum limit of the DC imposition magnitude is determined by safety operating limits and also controlled to less than the pulsating wave peak voltage. The negative and positive polarity may be set permanently or may be controlled by switching the terminal polarity either at a pre-programmed frequency or manually.

(50) As discussed above, the basic waveforms of a DC superimposed time-varying frequency wave can be of square, triangular, sine or other random form and the final output of the DC superimposed time-varying frequency wave can be in any one of the combinations shown in FIGS. 5 to 9.

(51) The DC biased time-varying pulsed wave can be produced by an asymmetrical ULF wave or by use of inductive diode filters, conventional diodes or filtering circuits. When the ULF wave is asymmetrical or offset, the time varying AC wave will become a DC biased wave. The same filtering or rectifier components may also be used or added separately to create spikes in the waveform to enhance the disinfection performance.

(52) The DC superimposition for the present invention can be provided by any one of the following methods: 1. Using a Switch Mode DC power supply or other AC to DC rectifiers power supply with variable or fixed output voltage. 2. If using inductive diode filters, the DC imposition is achieved by filtering all or part of the positive or negative half of the AC wave amplitude hence biasing the wave amplitude toward only the positive or negative direction. 3. A rechargeable DC battery can also be used for DC superimposition purpose, in place of the inductive diode filter or the DC. 4. By using a specific circuitry design to produce a desired asymmetrical AC pulsed time-varying wave.

(53) The pulsating wave frequency range may be from 100 Hz to 1 MHz, and is preferably between 0.1 kHz to 200 kHz.

(54) The sweeping frequency of the pulsating frequency range may be any value between 1 and 1000 Hz.

(55) As discussed above, when the system is installed in a metallic piping or housing system 640, the metallic housing can be used as the wave returning emitter 660.

(56) As discussed above, the wave emitting emitter 620 materials may also be chosen from consumable or non-consumable materials. If a consumable material is chosen, such as magnesium or aluminum anodes, this provides the added advantage of not producing chlorine.

(57) A further aspect of this invention comprise the use of a new composite electrode using steel rod wrapped with MgCO.sub.3+MgO or other alkali materials which provides an alkaline environment will be able to produce an in situ generated magnetite layer on the steel anode surface. Such an electrode has been used with DC current to generate the magnetite but this has the disadvantage that Fe.sub.2O.sub.3 is often produced before the magnetite production. As a result, the steel rod will still be consumed and the objective of forming a permanent electrode is hard to achieve. In the present invention, the steel rod is energized with the DC biased time-varying pulsating wave and, due to the presence of the pulsating wave instead of a static DC current, the magnetite is able to form very effectively on the steel rod, due to the higher energizing energy effect from the pulsating wave. To further enhance the magnetite formation, the steel rod may first be pre-energized using a DC biased time varying wave by connecting it to a temporary wave emitting emitter. When the steel rod receives DC biased time varying wave current from the temporary wave emitting emitter in the MgO+MgCO.sub.3 alkaline environment, a magnetite layer will form readily on the steel rod. After forming the magnetite, the steel rod is disconnected from its position as a wave returning emitter and it can then be used as a long-lasting permanent magnetite emitter.

(58) The use of consumable, semi-consumable or permanent wave emitter and returning emitters, and combinations in the treatment system can be arranged in many possible arrangements or modified as required to suit various onsite conditions. In general, the wave emitter and returning emitter assembly can be part of the usual piping system of the treatment system or they can be arranged in a separate wave emitter/returning emitters chamber.

(59) In the system and methods of the invention, TRO in the water is controlled or mitigated by the DC superimposition amount. The DC superimposition control may be controlled manually or via an automatic TRO concentration feedback controller to suit ballast water treatment requirements or other applications.

(60) There are many situations when a ship has to navigate in water with unknown sudden changes in conductivity such as navigating from fresh water to sea water and vice versa. Under such circumstances there will be sudden changes in conductivity such that the current output may increase drastically when navigating in high conductivity water or the output current will be too low when the ship is in a fresh water river or lake. Conventionally, a constant current transformer may be used to control the current. However, the constant current transformer regulates the current output by varying the voltage and in the situation of high conductivity seawater, the voltage will need to drop to only a few volts compared with a high of, say, 48V in fresh water to avoid over-current. This is because seawater conductivity can be as high as 50 ms/cm and fresh lake water can have a conductivity of as low as 0.1 ms/cm. When the voltage drops to a low of only a few volts, it is too low and insufficient to create the organism kill effect. Similarly, if a maximum current is set to accommodate the maximum current under high salinity conditions, then in fresh water conditions the voltage is maintained at maximum but the current is too low to create the kill effect, due to the constant current transformer rectifier control function.

(61) To overcome the above problem, in this invention, a Pulse Width Modulation method may be used. In this embodiment, the predetermined effective kill voltage and current are first set into the program for the lowest conductivity condition. When the conductivity increases, the pulse band width is reduced to reduce the current root mean square value yet the voltage is maintained constant. In this way, the organisms in the water will be subjected to the required voltage and current treatment and hence a good disinfection effect can be produced or maintained under all kinds of water conditions.

(62) For all the embodiments of the invention the generation of the time-varying DC pulsating wave is as described above and consists of superimposing a direct current on a low frequency time-varying pulsating electromagnetic wave signal. The low frequency time-varying electromagnetic wave can be in sine, square, triangular or even in random form. However, the frequency range preferably operates in the range from 100 Hz to 1 MHz and varies with a sweeping frequency of 1 to 1000 Hz. The selection of the range of frequency and also the sweeping frequency will be determined by the fluid quality, flow rate, and treatment purpose.

(63) The invention thus provides a system and a method for applying a superimposed time-varying frequency electromagnetic wave to ballast water and ballast water treatment systems which is very simple, relatively inexpensive, and more environmentally sound. Most importantly, it meets the USCG requirement yet with a relatively low power consumption which is available on board ship without the need to install an additional generator.

(64) Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options of all other aspects, features and parameters of the invention.

(65) While the embodiments described herein are intended as exemplary systems and methods, it will be appreciated by those skilled in the art that the present invention is not limited to the embodiments illustrated. Those skilled in the art will envision many other possible variations and modifications by means of the skilled person's common knowledge without departing from the scope of the invention, however, such variations and modifications should fall into the scope of this invention.