WO2011031239A1

WO2011031239A1 - System for the disinfection of ballast water

Info

Publication number: WO2011031239A1
Application number: PCT/SG2010/000332
Authority: WO
Inventors: Jiaping Paul Chen; Yu-ming ZHENG; K. G. Nadesshani Nanayakkara; Khorshed Alam Akm
Original assignee: National University Of Singapore; The Maritime And Port Authority Of Singapore
Priority date: 2009-09-08
Filing date: 2010-09-08
Publication date: 2011-03-17
Also published as: SG179013A1; WO2011031239A8

Abstract

A disinfector for disinfection of ballast water comprising a housing having an inlet and outlet for the transmission of ballast water through the housing; a plurality of electrodes in the housing representing anode and cathode electrodes; wherein each of said electrodes includes an array of apertures distributed over at least a portion of the electrode so as to permit the ballast water to flow through the electrode.

Description

SYSTEM FOR THE DISINFECTION OF BALLAST WATER

Field of the Invention The invention relates to environmental issues surrounding shipping, for instance ballast water management.

Background

Maintaining the stability and the structural reliability of ship during the voyage is essential to ensure the safety of the ship and the crew. Ballast is used to maintain the balance of ships. The ballast is particularly important when a ship is empty of cargo. In the past, solid materials such as rocks and sands are used as ballast. Modern ships use water as ballast.

The ballast water (BW) carries many unwanted marine species, oil and grease (O&G), organics, and solids. Typically, the marine species include bacteria and other microbes, planktonic species, small invertebrates and the spores, eggs and larvae of larger species. The survival of these microorganisms depends on many factors. Some species are able to survive to form viable populations. Once survived in the journey and introduced to a foreign environment, those organisms can become invaders to the new environment. Newly-established species are harmful to human health (e.g., vibrio cholerae), and to the bio-diversity of marine environment.

The amount of ballast water carried in ships per year can be as high as 10 billion tons per year. It is estimated that in the USA alone, the cost of all invasive species exceeds several hundred billion USD per year.

The international marine organization (IMO) had enacted a regulation that all the new built ships must have ballast water treatment system from 2012, and all the existing ships must install ballast water system by 2016. Due to the strict regulations enforced by national and international agencies, the market for ballast water management system (BWMS) is growing rapidly. The discharge rates of ballast water can be very high over short periods of time. The traditional way in which engineers have usually used is to design a buffer facility in the system. However, such design often leads to a large increase in the size of the system and fails to take into account of possible changes in the quality of water while it is still in the buffer. Moreover, there may be instances where for economic reasons, it would be desirable not to buffer but to discharge as quickly as possible.

Current technologies for ballast water treatment are typically based on systems with buffer capacities. Most of the studies in literatures are limited to small-scale test where the ballast water is treated by either ex-situ (outside ballast tanks) or in-situ systems (within ballast tanks), involving both physical and chemical treatments. The processes include granular media filtration, thermal treatment, UV irradiation, ozone treatment, chlonnation, membrane filtration, and advanced oxidation. While good inactivation of the microorganisms is reported, the treatment efficiency for O&G and solids remains unacceptable. In addition, the hydraulic retention time of existing technologies is often high. As ballast water has an extremely high flow rate often ranging from 600 to 1000 m /hr, the current technologies may not be suitable. Hence, this invention aims to disclose a cost-effective technology for ballast water treatment by employing electrochemical technology.

Summary of Invention In a first aspect the invention provides a disinfector for disinfection of ballast water comprising a housing having an inlet and outlet for the transmission of ballast water through the housing; a plurality of electrodes in the housing representing anode and cathode electrodes; wherein each of said electrodes includes an array of apertures distributed over at least a portion of the electrode so as to permit the ballast water to flow through the electrode.

In a second aspect the invention provides a disinfector for the disinfection of ballast water comprising a housing having an inlet and outlet for the transmission of ballast water through the housing; a plurality of electrodes in the housing representing anode and cathode electrodes; wherein each of said electrodes is made from a titanium member having a metal oxide coating. In a third aspect the invention provides a water management system comprising a water source for the supply of water to be disinfected; a disinfector for disinfecting said water, said disinfector comprising a housing having an inlet and outlet for the transmission of the water through the housing; a plurality of electrodes in the housing representing anode and cathode electrodes for eletrolytically disinfecting said water as it is transmitted through the housing; a water delivery system for removing the water for disposal; and a neutralization system arranged to detect the concentration of TRO within said disinfected water and inject a neutralizing chemical into said water before disposal.

In a fourth aspect the invention provides a method for disinfecting water comprising the steps of: transmitting water to be disinfected through a housing having a plurality of electrodes in the housing representing anode and cathode electrodes; eletrolytically disinfecting said water as it is transmitted through the housing;

delivering said water to a tank; detecting the concentration of TRO within said disinfected water; inject a neutralizing chemical into said water before disposal of said water.

In a fifth aspect the invention provides a disinfector for disinfection of wastewater comprising a housing having an inlet and outlet for the transmission of wastewater through the housing; a plurality of electrodes in the housing representing anode and cathode electrodes; wherein each of said electrodes includes an array of apertures distributed over at least a portion of the electrode so as to permit the wastewater to flow through the electrode

Brief Description of Drawings

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 A is a schematic view of a ballast water management system according to an embodiment of the present invention;

Figure IB is a schematic view of the ballast water management system according to

Figure 1 A during the ballasting process;

Figure 1C is a schematic view of the ballast water management system according to Figure 1 A during the de-ballasting process;

Figure 2A is an elevation view of an electrode for a reactor according to one embodiment of the present invention;

Figure 2B is a schematic view of a reactor according to a further embodiment of the present invention;

Figure 3 is an SEM image of an electrode according to a further embodiment of the present invention;

Figure 4 is an SEM-EDX characteristic of the electrode of Figure 3;

Figures 5A and 5B are elevation views of electrodes according to the prior art; Figures 6A is a graph of experimental data of a reactor according to a further embodiment of the present invention;

Figure 6B is a comparison of idealized and actual reactor performance;

Figure 7 is a graph of voltage variation of an electrode according to a further embodiment of the present invention;

Figure 8 is a graph of chlorine production of an electrode according to a further embodiment of the present invention;

Figures 9A to 9D are SEM images of electrodes after 8 days of continuous use; Figure 10 is a graph of electrode performance comparing one embodiment of the present invention to a prior art electrode.

Detailed Description Figures 1 A to 1C show an embodiment of the Ballast Water Management System

(BWMS) according to one embodiment of the present invention. As abovementioned, the processes of ballasting and de-ballasting have been recognized as a threat to the coastal environment due to the possible introduction of invasive organisms via ballast water and coastal sediments which are pumped in with ballast water. The major aim of the invention is to develop a cost-effective electrolysis technology for ballast water treatment. The focus is on the design of electrodes and disinfector that play key roles in the treatment.

The ballast water management system (BWMS) 2 is accomplished by using filtration, electro-disinfection and neutralization of the residual oxidant. The schematic diagram of the process is shown in Figure 1A. The inlet 4 and pump 10 act as a water source for the supply of infected water to the BWMS.

The first unit in the treatment is filtration 22. The filtration by using at least one self- cleaning micro-strainer (with size of 5 to 100 um) during the intake 4 process is to ensure to effectively remove organisms and solids, and reduces sediment built-up in the ballast water tanks, which is a potential area for survival and growth of organisms and microorganisms. It may remove various bio-solids (colloidal substances), which can lead to formation of disinfection byproducts (DBPs) in the presence of chlorine. With the filtration system, the amount of disinfectants required will be reduced and the concentrations of DBPs can also be reduced.

As shown in Figure IB, the filtration is only operated during the ballasting. The operation and cleaning of the micro-strainer(s) is (or are) fully automatic without interrupting the filtration process, and the backwashing water may be returned into the sea in situ or stored in waste storage tank in the ship.

The followed electrochemical reactor 28 (also termed as reactor, disinfector, electro- disinfector, or electrolysis unit) is to produce disinfectants (chlorine, 0₃, hydroxyl radical and other free radicals) for the disinfection. Some of microorganisms (e.g., E. coli) in the ballast water can be directly killed in the disinfector 28, while others are disinfected by residual oxidants in the ballast water tank. The total residual oxidants (TRO) is produced by the disinfector 28 and its concentration is no more than 12 mg/L (TRO as chlorine), which can kill the microorganisms in the ballast tanks and prevent them from the re-activation during the voyage of ship. This value is confirmed by a series of experimental studies (lab- and pilot-scale experiments) for various seawaters (from slightly contaminated to heavily contaminated seawater).

The disinfectants are generated by the electrolysis of the seawater! in the electrochemical reactor 28 by the titanium based electrodes. The TRO is measure by a TRO analyzer and controlled at a pre-set value through a computer.

The electrochemical reactor system is composed of: rectifier 24, chiller 26, electrodes, control computer 38, TRO analyzer 36, and flow transmitter. As seawater is corrosive, corrosion-proof materials will be used for the construction of the reactor. Chiller 26 may be needed so as to reduce the heat generated by the rectifier 24.

The last treatment unit is to neutralize the residual oxidant. Before de-ballasting, as shown in Figure 1C, a neutralization solution (sodium thiosulfate) is injected to remove the residual oxidants in order that the TRO after the neutralization will be no more than 0.1 mg/L (as Cl₂) (maximum allowable concentration). The dosage of sodium thiosulfate is calculated by:

[Na₂S₂0₃] (mg/L) = [residual oxidant (as chlorine)] x factor

The concentration of residual oxidants (mg/L, as chlorine) is determined by the TRO analyzer 36, which provides the real-time measurement. The factor is 0:65 - 0.75. The neutralization system 12 is composed of chemical storage vessel, and the metering pum for chemical injection.

i₍

The operation and monitoring of the BWMS are controlled by a computer system

38. Ballasting Process: Valves 18 and 40 are closed. Valves 8, 16 & 30 are opened. The seawater is transmitted the strainer 6, valve 6, pump 10, valve 16, self-cleaning micro-strainer 22, electrochemical disinfector 28 and valve 30 in series, and then fills in the ballast tank 32. The process is shown in Figure IB. The ventilation 34 is turned on so that the hydrogen gas and chlorine gas generated in the electrolysis can quickly be removed, even though both concentrations are extremely low, demonstrated in the theoretical calculation and experimental measurement.

De-ballasting Process: Valves 8, 16 & 30 are closed. Valves 18 and 40 are opened. The seawater is pumped for disposal from the ballast tanks 32, and goes through Valve 40, pump 10, and Valve 18 in series, and then is discharged. The TRO analyzer 36 will determine the TRO level so that the dosage of sodium thiosulfate can be determined. The neutralization solution is then injected 12 before the pump, and so before final disposal of the water, to remove the TRO to below 0.1 mg/L. The neutralization concentration is determined by the above equation. The process is illustrated in Figure ic

Management of chemical: Sodium thiosulfate (Na₂S₂0₃) is the only chemical required for storage and handling. In the proposed BWMS, sodium thiosulfate is stored in stainless steel tank that will be designed and manufactured according to the international design code. As the dosing system is automatic, there is no personal contact of the chemical.

The amount of sodium thiosulfate stored is dependent upon the frequency of ballasting and de-ballasting operations, and total ballast capacity of the vessel. For example, for neutralizing ballast water with 1000 m³ and TRO (as chlorine) of 10 mg/L, the amount of sodium thiosulfate is 7.5 kg (assuming the above factor of 0.75). In the reality, the amount will far below because the TRO of the water for the de-ballasting is expected to range from 0 to 1 mg/L due to the consumption in the disinfection and the natural decay. If the TRO is 1 mg/L and the water volume is 1000 m³, for example, the amount of sodium thiosulfate is only 750 grams.

Proper personal protective equipment (PPE) will be used. Only properly trained technicians will be allowed to perform the chemical re-supply. The subject of the present invention is the disinfection unit 28, including the electrodes used by the disinfection unit to produce the necessary disinfection solution. For instance, Figure 2 A shows one embodiment of the electrode 70 according to the present invention, here is demonstrated a sheet 75 having an array of apertures or perforations arranged to allow the flow of ballast water to pass through the electrode 70. This arrangement provides substantial advantage in flow characteristic within the reactor reducing hydraulic shock losses, whilst still maintaining contact with the ballast water to produce the electrolyzing effect. Whilst this embodiment shows the array of apertures being uniformly distributed, and covering the entire sheet, it will be appreciated that the array does not necessarily need to cover the entire sheet, but will need to cover a substantial proportion. Further, whilst a uniform array may assist in manufacturing, for the functional purpose of the electrode, thee array does not need to be uniform, but may be a non-uniform array.

In the embodiment of Figure 2 A, a further advantage is the use of an expanded slit sheet. Whilst a simple sheet having apertures placed therein provides the flow characteristics, the expanded slit sheet also increases surface area exposed to the ballast water, whist also saving material. Given the high cost coatings applied to electrodes, having the perforations formed through slits 80 compared to removal of material to form the apertures may^÷ provide a substantial cost saving.

It will be appreciated that the electrode may be formed in a number of different ways, such as the expanded slit sheet shown in Figure 2A, a perforated sheets or a mesh. In order to allow the direct transmission or flow, of ballast water through the electrodes, the aim is to reduce the pressure drop across the disinfector, or reactor. Notionally, the percentage of apertures, or holes, in the electrode may be about 50%, but may vary 30% depending on the application. A pressure drop (resistance) across the disinfector may be insignificant and will not reduce the pressure (driving force) of water that is in the range 1 to 2 bar. By specifying a range of aperture percentages and/or pressure drop, the designer will be able to apply the invention to a range of different situations. Figure 2B shows a possible arrangement of a reactor 71 having a plurality of electrodes 76, and showing the transmission of ballast water through the housing 72. In this case, the electrodes for the anode 74 and the cathode 73 are alternately placed. Figure 2B further shows the benefit of the array of apertures in the electrode. As ballast water 77 enters the housing 72 of the reactor 71 , the electrodes provide a barrier, dividing the flow 78. However, the apertures provide flow paths through the electrodes, and consequently, the flow path of the ballast water through the housing is direct, and not a meandering path around the electrodes, until the flow exits 79 the housing. Thus, shock losses reducing the efficiency of the flow are reduced, without detrimentally affecting the disinfecting function of the reactor.

For the disinfector 71 of Figure 2B a free space 81 is provided adjacent to the outlet. This permits a residence time for the ballast water to fully mix and more completely disinfect the water. In a further embodiment, the electrodes 76 may extend up to the outlet, and so eliminating the space 81. This could be advantageous for space limitations, or where the number of electrodes is sufficient for mixing and disinfecting, and so not requiring the space.

In a further aspect of the invention, the electrode 70 may be is composed of metals and metal oxides. For instance, the coating of the electrode may include Ruthenium Oxide, Titanium Oxide, Iridium Oxide or Lead Oxide. This coating may provide the advantages of:

i) Producing disinfectants with low energy consumption;

ii) Extended longevity of the electrodes;

The thickness of coating layer comprised of Ru oxide, Ti oxide etc may be in the range 1 μιη to 10 μηι. In a further embodiment, the coating may be 3 to 4 μπι.

The diameter of rod is typically 1 to 3 mm. The geometry can be octagon, oval, parallelogram, trapezoid, pentagon, rectangle, circle, square, and combination of the any two. In the current invention, the main electrochemical disinfector is capable of producing disinfectants on-site to inactivate the microorganisms. Disinfectants such as chlorine, hypochlorous acid, sodium hypochlorite, ozone, and free radicals are produced on-site using the abovementioned reactor.

For improved performance, a housing for the electrochemical disinfector may be rectangular or cylindrical typed with the ratio of length to the greatest cross-sectional dimension of above 5 (i.e. L/D > 5, L/H>5, and L/D>5). Examples of the greatest cross- sectional dimension include the greater of width and height for a rectangular prism, diameter for a cylinder, or primary axis for an ellipsoidal prism.

The length of the reactor may be calculated based upon the design flow rate of ballast water through the reactor, and the desired residence time of the ballast water exposed to the electrodes. Accordingly, the dimensions of reactor may be calculated based on the BWMS design specification.

There are two types of reactors that can treat water continuously: a) continuously stirred tank reactor (CSTR), and b) plug flow reactor (PFR). The equations of continuous flow reactors are compared in Table 1. Since the order of disinfection reaction kinetics is above one, the time (τ) to reduce a concentration of microbial species from Co to C_e using PFR is less than CSTR. In other words, the PFR

outperforms the CSTR in the BWMS.

Table 1 Performance of disinfection by two reactors

Whilst not mandatory for the invention, there are particular advantages in using a PFR. However, the ideal PRF cannot be obtained due to the limited space available in ship. Thus, the above ratio has been experimentally obtained so as to maximize the efficiency of the electrochemical disinfector.

The experimental results further confirm our design (the ratio of length to width, height and diameter of above 5). As shown in Figure 6B, one would see the difference between the ideal PRF and non-ideal PRF. Figure 6A shows that the electrochemical disinfector based on our design can achieve the non-ideal PFR, leading to excellent treatment results shown in the disinfection experiment.

The effective volume (V, m ) of the reactor 28 is calculated according to Equation (1).

V=Q x (0.1~5)*10^'3 (1) where Q (m³/h) is the flow rate of the ballast water. The reactor consists of electrodes: anodes and cathodes. Inner metal (titanium) mesh/plate and/or inner metal coated with metal oxide layer (ruthenium oxide, iridium oxide, lead oxide or their combination) are used as the electrodes. The electrodes are placed perpendicular to the water flow. The area (A, m ) of electrodes can be determined by Equation (2):

A=Q x (0.005-0.1) (2) The applied current (I, A) can be estimated by Equation (3): I = Q x (l~20) (3) The power consumption (W, kwh) for the disinfection reactor can be calculated according to Equation (4):

W = Q* (0.004-0.1) (4)

Experimental data

The elements on one of electrodes developed by the inventors were analyzed with the results given in Table 2, and Figures 3 and 4. As shown, the Ru is one of key elements on the electrode.

Table 2 Key Elements from a Surface Scan of the Electrode Coating

Based on the design of the invention, an electrochemical disinfector was fabricated. The flow behavior was experimentally determined. Figures 6A and 6B, are an analysis of the flow behavior in the reactor, with Figure 6A being experimental results of the designed reactor system, and Figure 6B being flow patterns for ideal and non-ideal plug flow. As can be seen, the behavior of the disinfector is very similar to the non-ideal plug flow reactor under different flow rate.

In this invention, the water fully flows through the electrochemical disinfector (called as flow-through). The water may also be disinfected by the so-called side-stream method, whereby a proportion of the entire flow is divided from the main line, and subjected to a disinfection process. In the disinfection by both systems (flow-through and side-steam), chlorine is produced and kills microorganisms. Additionally, short-life chemically powerful oxidants (disinfectants) (mainly free radicals) may play a key role in the killing of microorganisms when the flow-through mode is used.

To evaluate the contributions (and effects) of free radicals (which are short-life) on the disinfection (operated by the flow-through mode), iso-propanol, a well-known OH^" radical scavenger was used. Prior to the tests, it was found that the used iso-propanol has no effect on the biological growth of E. coli and its killing/inactivation. In order to avoid any influence caused by the presence of chloride and chlorine, Na₃P0₄ was used in the study.

Table 3: Effect of OH' free radical on disinfection of E. col

As shown in Table 3, for both Ru0₂ coated Ti mesh and Ti mesh, the disinfection efficiency drops greatly after adding the radical scavenger. This finding confirms the powerful effect on disinfection from the generated OH^' radicals. In other words, the disinfection by the flow-through method in this invention is more powerful than that by the side-stream method.

An electrode according to the present invention and a standard Ti electrode were studied in terms of corrosion, chlorine production and stability to establish the longevity effects offered by the present invention. Ti mesh is capable of producing enough disinfectants and inactivate E. coli and E. faecalis successfully. Nevertheless, one of the major operational problems associated with the use of Ti mesh in long-run was identified during continuous usage of Ti mesh electrode. Anode 105 is dissolved 110 in seawater electrolyte after two days of continuous operation at 0.04 A as shown in Figure 5A. The cathode 115 has deposits 120 due to the coating of Ca and Mg precipitates, as shown in Figure 5B. Therefore, the Ti electrode cannot be used for a long time and thus limits its applications.

The Ru0₂ coated electrodes were used as both anode and cathode in a batch reactor and continuously operated for 8 days at 0.04 A in seawater. No visual damages were observed at the end of the operation. Moreover, the operating voltage did not change significantly during the investigation, as shown in Figure 7, suggesting the electrode is very stable in electrolysis of seawater. The performances of three electrodes of our invention were tested for the chlorine production. They are virtually the same type of electrode; the only differences are that, one is new and not used, one is used but without being cleaned, and the last one is used and cleaned before testing. Figure 8 shows that the used electrodes (particularly the used electrode) outperform the new electrode in the chlorine production. The used electrode that was not cleaned is slightly better than the used electrode that was cleaned. As shown in Figures 9A to 9D, more pores are developed on the anodic electrode 135 (anode used for 8 days). Take note that, in the figure, 145 is a new electrode in seawater for 8 days on which the electricity was not applied, 140 is a cathode operated for 8 days, and 150 represents a new and un-used electrode. As more pores are generated after a period of time (e.g., 8 days in the figure), more surface areas for chlorine production become available and thus more chlorine is produced as indicated in Figure 8.

Figure 10 shows the production of chlorine by an electrode 155 according to the present invention as compared to a Ti electrode 160. It is clear that the electrode 155 according to the present invention can produce more chlorine than Ti electrode 160. Type Weight loss (g) Corrosion rate (mm/ r) ballast water 0.062 (after 4days) 0.0156 chlorinated ballast water 0.065 (after 4days) 0.0157

Table 4 Results of corrosion study

A corrosion study was performed with the data given in Table 4. As shown the system in the invention does not cause serious corrosion to the ballast water tank.

The electrode in this invention is highly stable and catalytic towards the production of chlorine and other disinfectants, as shown in Figures 7 and 8. At the same time, the energy consumption is lower than many other electrodes, as shown in Figure 10.

In the current invention, level of residual disinfectants (TRO) coming out of the disinfector is maintained at a range from 1 to 12 mg/L, so that the issues such as corrosion and chemical safety are minimized. A series of bench- and pilot-scale studies were conducted. The experimental results show the treated ballast water can meet the IMO regulation (G8). For example, at a flow rate of 10-12 m³/hour, E. coli and Intestinal Enter ococci concentrations reduced to 3 CFU/100-ml and <1 CFU/100-ml, from 10⁵-10⁶ CFU/100-ml and 10³-10⁴ CFU/100-ml, respectively, with an energy consumption of 0.06 kWh/m³; the total residual oxidant (as chlorine) concentration is 2 to 3.5 mg/L. The killing of microorganisms is permanent and no re-activation is observed. The energy consumption and foot-print are much lower than reported commercial BWMSs.

In a further embodiment, the electrodes may be de-scaled through polarity switching. In this process, the polarity of the electrodes may be switched, that is the potential on the cell reversed such that the anode becomes the cathode and the cathode becomes the anode. This switching may occur periodically, for instance every 5 to 10 minutes. This has the benefit of avoiding the cost of pre-treatment, as well as post- treatment of the electrodes to remove the scale physically.

It will be appreciated that whilst ballast water treatment is a significant application for the present invention, it may also be used for disinfection of wastewater, of which salinity is high enough to conduct electricity.

Claims

Claims:

A disinfector for disinfection of ballast water comprising

a housing having an inlet and outlet for the transmission of ballast water through the housing;

a plurality of electrodes in the housing representing anode and cathode electrodes;

wherein each of said electrodes includes an array of apertures distributed over at least a portion of the electrode so as to permit the ballast water to flow through the electrode.

The disinfector according to claim 1, wherein the distribution of apertures is uniform.

The disinfector according to claim 1 or 2, wherein the array of apertures in the electrodes provides a direct flow path for the ballast water from the inlet to the outlet.

The disinfector according to claim 3, wherein the anode and cathode electrodes sequentially alternate along the flow path.

The disinfector according to any one of the preceding claims, wherein each electrode is formed from: an expanded slit sheet, mesh or perforated plate.

The disinfector according to any one of the preceding claims wherein the ratio between the length and greatest cross-sectional dimension of the housing is greater than 5.

7. The disinfector according to claim 6, wherein the housing is the shape of one ; of: a cylinder, rectangular prism or ellipsoidal prism.

8. A disinfector for the disinfection of ballast water comprising

wherein each of said electrodes is made from a titanium member having a metal oxide coating.

9. The disinfector according to claim 8, wherein the metal oxide coating is any one or a combination of: ruthenium oxide, iridium oxide, titanium oxide or lead oxide.

10. The disinfector according to claim 9, wherein the coating has a thickness in the range 1 to 10 um.

11. The reactor according to claim 8 to 10, wherein each of said electrodes includes an array of apertures distributed over at least a portion of the electrode so as to permit the ballast water to flow through the electrode.

12. A water management system comprising

a water source for the supply of water to be disinfected;

a disinfector for disinfecting said water, said disinfector comprising a housing having an inlet and outlet for the transmission of the water through the housing;

a plurality of electrodes in the housing representing anode and cathode electrodes for eletrolytically disinfecting said water as it is transmitted through the housing;

a water delivery system for removing the water for disposal;

and a neutralization system arranged to detect the concentration of TR.0 within said disinfected water and inject a neutralizing chemical into said water before disposal. The system according to claim 12, wherein the water is ballast water and the water source system includes a seawater inlet having a pump for drawing said seawater into the system.

The system according to claim 12 or 13 wherein the neutralization system is arranged to detect the concentration of TRO and inject the neutralization chemical during disposal.

A method for disinfecting water comprising the steps of:

transmitting water to be disinfected through a housing having a plurality of electrodes in the housing representing anode and cathode electrodes;

eletrolytically disinfecting said water as it is transmitted through the housing;

delivering said water to a tank;

detecting the concentration of TRO within said disinfected water;

inject a neutralizing chemical into said water before disposal

of said water.

The method according to claim 15, wherein the water is ballast water and the water source system includes a seawater inlet having a pump for drawing said seawater into the system.

The method according to claim 12 or 13 wherein the detecting and injecting steps occur after removal of said water from the tank and before disposing of said water.

The method according to any one of claims 15 to 17, further including the step of reversing polarity of the electrodes within the housing for a predetermined period, so as to remove scale from said electrodes. A disinfector for disinfection of wastewater comprising

a housing having an inlet and outlet for the transmission of wastewater through the housing;

wherein each of said electrodes includes an array of apertures distributed over at least a portion of the electrode so as to permit the wastewater to flow through the electrode.