WO2011016781A1

WO2011016781A1 - Emissions control system and method

Info

Publication number: WO2011016781A1
Application number: PCT/SG2010/000291
Authority: WO
Inventors: Paul Chen Jianping
Original assignee: The Maritime And Port Authority Of Singapore; National University Of Singapore; American President Lines Co Pte Ltd
Priority date: 2009-08-03
Filing date: 2010-08-03
Publication date: 2011-02-10
Also published as: KR20120139663A; SG178259A1; CN102933504B; KR101803368B1; CN102933504A

Abstract

A treatment system comprising an electrolytic cell, having an anode compartment and a cathode compartment, said electrolytic cell having an inlet for receiving salt water, said cell arranged to produce an alkaline solution within the cathode compartment and a disinfecting solution within the anode compartment; an alkaline scrubber unit for the treatment of exhaust emissions from a ship-mounted engine, said alkaline scrubber unit for receiving the alkaline solution and the exhaust emissions into a first chamber for mixing the exhaust emissions and alkaline solution mix, and; a disinfection unit intermediate a water inflow and a ballast tank, said disinfection unit arranged to receive the disinfecting solution and water from the water inflow so as to disinfect said water before delivery to the ballast tank.

Description

EMISSIONS CONTROL SYSTEM AND METHOD

Field of the Invention

The invention relates to environmental issues surrounding shipping, for instance the control of engine emissions and ballast water management.

Background

Stability of the ship is essential in order to ensure the safety of the ship and the crew. For this purpose, ships use "ballast water" during the voyage. Although there is a possibility of using solid materials (e.g. sand and rock) as ballast, water (including both seawater and fresh water) has been in use due to the convenience in ballasting and de- ballasting since the 1880s (Carlton, 1985). It is estimated that three to twelve billion tons of ballast water are discharged annually over the world (Rose, 2005).

Ballast water is discharged in high volumes in many parts of the world. The ballast water has been recognized as a threat to the coastal environment. Invasive organisms are introduced via ballast water and coastal sediment which are pumped in together with the seawater. A wide variety of organisms including bacteria and other microbes, eggs, cysts and larvae of various species are among the marine species that can be carried in with ballast water. Newly-established species can be harmful to human health (e.g., vibrio cholera) and may become a threat to the bio-diversity of marine environment and thereby lead to environmental, economical and healthy impacts.

Concerns towards the non-native organism transfer by ships' ballast water have increased since the late 1980s (Drake et al., 2007). The discharge rates of ballast water can be very high over short periods of time. The traditional way that engineers have usually used is to design a buffer facility in the system. However, such a design often leads to a large increase in the size of the system and fails to take into account the possible changes in the quality of water while it is still in the buffer. Moreover, there would be instances where for economic reasons, it would be desirable not to buffer but to discharge as quickly as possible.

Some research institutions and companies are developing ballast water treatment (BWT) technologies. Treatment technologies such as heating (Rigby et al., 1999), UV irradiation with pre-treatment (Sutherland et al., 2001), membrane filtration, chlorination (Zhang et al., 2001; da Silva et al., 2004), electro-ionization, electrolysis, and ozonation (Herwig et al., 2006) have been studied. Table 1 shows some of available technologies for ballast water treatment.

Heat treatment technology is proposed by a number of research groups. The toxic dinoflagellates are larger marine organisms such as plankton but are commonly found in fresh water habitats. Their distribution depends on temperature and salinity. In laboratory scale studies, it is reported that the toxic dinoflagellates can be completely inactivated after 2 hours of contact time at 35°C. Some of the researchers tried to use shorter contact times such as few minutes for killing organisms up to an acceptable level at high temperatures such as 45°C. This technology can use waste heat from the engine of the ship for ballast water treatment. However, when it comes to the practical application, the main concern to the industry is whether the amount of heat generated is enough for the intended purpose. Moreover, full scale tests showed possible damages to ballast tank coatings by the heated water because higher temperature can greatly promote corrosion to the body of tanks. Ultra violet (UV) irradiation can disinfect various types of bacteria. However, UV alone cannot perform well as the turbidity of the ballast water is normally high and the disinfection time is often long. In addition, its installation in existing ballast tank is often considered less favourable to the ship owners, and the cost is generally high. Table 1 List of available ballast water treatment technologies

The electro-ionization involves exposing biota to reactive species of mixed oxidant gases. In laboratory-scale studies, it has been reported that over 90% of bacteria are killed in a 2-minute contact time. Onboard tests are yet to be done and the use of several large-size gas generators is a problem to be solved in this technology.

Ozonation has been reported as a solution to the ballast water problem. This technology is effective in killing microscopic organisms, but is less efficient in eliminating larger organisms. Large size ozone generators are required for the treatment of huge volumes of ballast water. Ozone and its byproducts may be toxic to humans. Thus, its operation is often unsafe.

Various types of biocides have been researched for the ballast water treatment. Due to practical difficulties such as the amount to be added to high volumes of ballast water in one ship, transportation of biocides and operation of treatment units are considered less favourable to the industry. In addition, the efficiency and the possibility of causing corrosion are very often concerned. For example, Husain and coworkers (2006) used carbon dioxide to control the growth of bacteria. The method seems to be effective in their laboratory-scale study. The foreseeable problems may include corrosion to the ballast water tank and low efficiency for larger living organisms and anaerobic bacteria. The above existing technologies have common drawbacks of lower removal efficiencies, longer retention time, higher probability of reactivation of disinfected organisms, and higher cost. The technologies are often based on pilot- or laboratory- scale tests and the flow rate in the studies is normally low. The ballast water has an extremely high flow rate. For example, one ballast water pump has a flow rate of up to 600 m³/hr. Most of the currently available BWT technologies may not be suitable. In addition, most of technologies require changes in the ballast tanks and/or other existing facilities in ships; these make the technologies less suitable to the industry. All these limit their full-scale applications in ballast water treatment.

The only feasible measure that remains practiced on ships is the mid-ocean ballast water exchange. In mid-ocean, the ballast water in the ship is replaced with open ocean water either by emptying and refilling ballast tanks or by flow-through dilution. The ballast water after the operation will contain less contaminants and thus cause less environmental pollution when it is discharged in the next port. Though it is quite effective, the problems of this technology include: incomplete removal of microbial contaminants, and safety. For example, some of organisms, especially microorganisms, are stuck to the structure of the ballast tank, and are difficult to remove.

Exhaust gases from a ship's engine is another emerging environmental problem. Exhaust gases consist of CO₂, NO_x, SO_x, CO, and particulate matter as shown in Table 2. NO_x and SO_x are highly acidic, and have larger Henry Law constants and are easily dissolved in the water. As a result, they form strong acids in water solutions, which are a major contributor to acid rain. Further, carbon dioxide is one of the most important green house gases. Due to the sharp increase in CO₂ concentration over the last 20-30 years, global warming has become one of the most serious environmental problems facing us. The International Maritime Organisation (IMO) has implemented regulations to manage and control some of the constituents. For example, SO_x emission is to be reduced progressively. Global sulphur cap is to be reduced from 4.5 % (which is the current regulation) to 3.5 % effective from 1 January 2012. Further, this may be reduced to 0.5 % effective from 1 January 2020. These percentages are more stringent for Sulphur Emission Control Areas (e.g. California, US). Sulphur cap for those areas will be reduced to 1.0 % from 1st of July 2010 and being further reduced to 0.1 % from 1 January 2015. Currently, heavy fuel with higher sulphur content (low cost) is replaced with fuel with lower sulphur content (high cost), which is obviously highly costly to the ship owners.

Adsorption and absorption technologies are commonly used for treatment of the exhaust gases. In the adsorption, adsorbents such as activated carbons can be used. However, factors such as regeneration of used sorbents make adsorption less attractive in maritime industry. In absorption, seawater is used to absorb the acidic gases through scrubber. This commercial scrubber technology is currently used by many ships in the world. The pH of seawater is around 8, which indicates very weak alkalinity. Thus, the efficiencies of neutralization of the acidic gases are low. Less than 20% of treatment efficiency is reported for the removal of SO₂. Thus, efficiency and foot-print of the scrubbers are less attractive. Development of novel technologies for gas treatment onboard will be of higher scientific as well as commercial value.

Table 2 Estimated contents of gaseous species in exhaust gases from diesel engines

Summary of Invention

In a first aspect, the invention provides a treatment system comprising an electrolytic cell, having an anode compartment and a cathode compartment, said electrolytic cell having an inlet for receiving salt water, said cell arranged to produce an alkaline solution within the cathode compartment and a disinfecting solution within the anode compartment; an alkaline scrubber unit for the treatment of exhaust emissions from a ship-mounted engine, said alkaline scrubber unit for receiving the alkaline solution and the exhaust emissions into a first chamber for mixing the exhaust emissions and alkaline solution mix, and; a disinfection unit intermediate a salt water inflow and a ballast tank, said disinfection unit arranged to receive the disinfecting solution and salt water from the salt water inflow so as to disinfect said water before delivery to the ballast tank.

In a second aspect, the invention provides a method of treatment, said method comprising the steps of: delivering salt water to an anode and cathode; electrolyzing the salt water and so producing a disinfecting solution at the anode and an alkaline solution at the cathode; delivering exhaust emissions from a ship-mounted engine and said alkaline solution to a first chamber; treating said exhaust emissions by mixing with the alkaline solution within said first chamber; delivering salt water from an inflow and the disinfecting solution to a disinfection unit, and; treating said salt water by mixing with the disinfecting solution within said disinfecting unit.

The invention is therefore directed to an electrolytic cell for producing an alkaline solution from the introduction of salt water to scrub the exhaust gases so as to yield a liquid which may be environmentally safe to dispose of, and to produce chemicals (including disinfection solutions such as chlorine, OCl^", HOCl etc.) to disinfect water entering, leaving and/or residing in the ballast tank so as to kill biota prior to de- ballasting into potentially environmentally sensitive locations.

In one embodiment, the invention provides an integrated technology for the treatment of both ballast water and exhaust gases. A series of electrolytic cells may provide disinfectants for the killing of microorganisms in the ballast water and for generating alkaline solution and reducing agent (Cl₂) for the removal of exhaust gases

(SO_x, NO_x and CO₂) in the scrubbers.

When a ship, with such a system installed, is parked in a port, the electrolytic cells are operated to produce a series of disinfectants that will kill the IMO regulated microorganisms to meet regulatory specifications with an extremely low energy consumption in the range 0.006 to 0.01 kwh/m³. When the ship travels in the sea and/or is parked in a port, the electrolytic cells can be operated in such a way that alkaline solution is produced, which neutralizes the gaseous species in the exhaust gas from the combustion in the engine(s). In addition, the stream containing chlorine from the electrolytic cells can oxidize NO in the exhaust gas. The removal efficiencies of the gases are much higher than currently available technologies.

It will be appreciated that, for vessels in fresh water, such as canals, rivers and lakes, fresh water may be used with salt is added, in order to provide the inflow of salt water to the electrolytic cell. For a fresh water application it will be necessary to add salt to the inflow in order to raise salinity to a required level. For instance, a salinity of 20 PSU may be required in order for the system to operate. The salt may be added to the inflow in a mixing zone, hi a further embodiment, the mixing zone may include a solution tank into which the fresh water flows, with salt added to the solution tank, to provide sufficient turbulence, residence time or other factor to satisfactorily dissolve the salt. A salinity sensor may be provided in the tank or proximate to an outlet in order to determine salinity of the water. The salinity sensor may be connected to a control system controlling the quantity of salt to the tank.

The advantages of the technology include: 1. a single system for treatment of both environmental hazards: ballast water and exhaust gas; 2. no chemicals needed to be shipped; 3. high efficiencies for removal of both hazards; 4. ease in operation.

In the operation of the treatment system, the electrodes of the electrolytic cell may be subjected to scale adhering to the surface due to the presence of magnesium and calcium within the water. This scale will adversely affect the operation of the electrolytic cell, reducing efficiency, and if left unchecked preventing operation. To mitigate this effect, the water may be pre-treated through an ion exchange process.

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 0.5 to 1 hour, for a limited time, such as for 5 to 190 minutes, until the electrodes are de-scaled, or substantially de-scaled. This has the benefit of avoiding the cost of pre-treatment, as well as post-treatment of the electrodes to remove the scale physically.

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 is a schematic view of an electrolytic cell according to one embodiment of the present invention;

Figure 2 is a schematic view of a scrubber system according to a further embodiment of the present invention.

Figure 3 is a schematic view of a ballast water treatment system according to a further embodiment of the present invention. Detailed Description

Figure 1 is a schematic view of an electrolytic cell 5 used to produce an alkaline solution for treating exhaust emissions, and a disinfection solution (such as chlorine, OCr, HOCl etc.) for treating ballast water. It should be noted that normally a series of electrolytic cells (multiple cells) may be required to be used so as to produce sufficient alkaline solution and disinfecting solution for exhaust gas and ballast water treatment. However, a single electrolytic cell may be sufficient only when the quantity of exhaust gas and/or ballast water is small.

The electrolytic cell includes an anode 20 and cathode 25 which are located in respective anode compartment 10 and cathode compartment 15 within the electrolytic cell 5. The compartments 10, 15 are separated by a membrane 65(e.g., diaphragm and ion exchange membrane). The electrodes can be Ti, and/or RuO₂ with minor component of IrO₂. MnO₂ may be used once when the production of Cl₂ is not required.

The technology can be used for seawater environment; it can also be used for the fresh water environment, where salt is added to the fresh water inflow. Ni coated Ti electrode may be used in the cathode compartment 15 for enhanced productions of alkaline solution and hydroxide ions.

The electrolytic cell 5 is arranged to receive salt water (such as sea water or fresh water with salt added) 30 through one inlet and outlet salt water (e.g., sea water) 40 with dissolve chlorine and/or oxygen.

The cathode 15 receives salt water 35 and delivers an alkaline solution of salt water with dissolved sodium hydroxide and hydrogen gas 58. The alkaline solution 58 passes through a gas/water separator 60 to remove the hydrogen 70, for venting to the atmosphere before directing the separated alkaline solution 56 through an outlet 45 for use in the scrubber system (shown in Figure T). It will be appreciated that any standard gas/water separator, capable of separating the hydrogen from the alkaline solution will be sufficient. The hydrogen gas may subsequently be collected and used for energy generation, including combustion or use with a fuel cell.

The ability to generate the chlorinated salt water (e.g. sea water) 40 and alkaline solution 56 from the respective compartments 10, 15 is provided through the membrane separation of said chambers.

When the treatment of exhaust gases is operated, for the anode compartment, one Valve 55 is closed while the alternate Valve 50 is open. The key reactions occur in the anode and cathode as follows.

In the anode 10, there is the following oxidation reaction: l/2Cl₂ + e^" = Cl^" Eo=1.391 v (Ia)

1/4O₂ + H⁺ + e^" = 1/2H₂O, E₀= 1.23 v (Ib)

In the cathode 15, the following reactions occur:

H₂O = 2H⁺ + OH^" (2a)

2H⁺ + 2e^" = H₂ (2b)

Due to the presence of the over-potential, the actual potential for Equation (Ib) is higher than (Ia). Thus, Equation (Ia) becomes dominant reaction. In other words, chlorine is produced in the anode compartment.

As hydrogen ions are consumed due to Equation (2b), the concentration of hydroxide (OH^") will increase because of Equation (2a). As a result, alkaline solution (mainly sodium hydroxide) is generated in the cathode compartment. It should be noted that that a gas-water separator 60 may be necessary for separation of hydrogen gas from the water from the cathode compartment 15.

The overall reaction is as follows.

2Cr + 2H⁺ = Cl₂ + H₂ (3)

The flow 40 from the anode compartment 10 (containing Cl₂) in Figure 1 can be used for removal of SO₂ and NO in the exhaust gases due to the reactions between these two gaseous species and Cl₂. The flow 45 from the cathode compartment with higher pH can further neutralize the acids (H₂SO₃, H₂SO₄, HNO₂, and HNO₃).

Further, the invention provides a system for the disinfection of ballast water entering, residing or exiting the ballast tank through mixing with a disinfecting solution produced by the electrolytic cell(s). One such disinfecting solution may be produced when, for the outlet from the anode compartment 10, one valve 50 is closed and the alternate valve 55 is opened. The chlorinated salt water 57 from anode compartment 10 will be mixed with the water 56 (high pH) from cathode compartment 15, leading to the formation of disinfectant (mainly OCl^", HOCl, and Cl₂) 45, to be used for the treatment of ballast water. Alternatively, the chlorinated water direct from the anode compartment 10 may be used as the disinfecting solution. During this operation, the NaOH produced by the cathode 15 may be stored for use with the scrubbers. Thus, the ballast water treatment may occur during the period the ship is in port, and more particularly during inflow and/or outflow of the ballast tanks. This may be a relatively short time compared with operation of the ship's engines. Hence, the storage requirements for the NaOH may be limited, and quickly used during the voyage of the ship between ports, or even when the engines are used to power the ship's operations within the port.

Because of other compounds in the water, other compounds may also form in addition to NaOCl 45, such as, but not limited to HOCl, Mg(OCl)₂, KOCl, Ca(OCl)₂, O₃ and free radicals all of which may contribute to the ballast water treatment.

In order to operate under the two different systems as shown in Figures 2 and 3, the electrolytic cell must be adaptable so as to change operation.

When a ship is traveling in the sea, huge amounts of exhaust gases are produced as shown in Table 2. The scrubber system is designed to achieve an enhanced removal of the exhaust gaseous species shown in the table.

As demonstrated in Figure 1, disinfecting solution and NaOH solution are produced by the electrolytic cell in the anode and cathode compartments and released from Outlets 40 and 45, respectively. As shown in Figure 2, the exhaust gases are treated by a scrubber system 75 comprising three different scrubbers 80, 85, 90, which use chlorinated water 40, then alkaline water 45, and finally water 95. The three scrubbers act as progressive stages in the treatment process with the exhaust emissions 100 passed into a (second) chamber of the chlorinated scrubber unit 80, and subsequently the remaining exhaust emissions passed 135 to the (first) chamber of the alkaline scrubber unit 85. The exhaust emissions still remaining are then passed 140 to a (third) chamber of the water scrubber unit 90 to be dissolved ready for final disposal 130, with any remaining gas vented 145. The treated liquid is discharged 110, 120 and 130 to the sea 150 after each stage 80, 85, 90, after mixing with a volume of water 105. As the discharged water 130 may still have a low pH, the addition of the water 105 may be used to dilute the acidity of the discharge 130 to raise the pH in the range 6 to 7 in line with international regulation. To this end, the added water 105 may be from any source, with the salt content immaterial to the purpose. Hence, for a fresh water application, no added salt is required for the dilution water 105 It will be appreciated that the chlorinated scrubber 80 and water scrubber 90 are optional to the invention, with the primary benefit for significant emissions control being provided by the alkaline scrubber 85.

The treatment of exhaust gases is performed in scrubbers that are normally installed and used in ship. The chemical reactions are listed in Table 3. With such a system, less and/or smaller scrubbers are needed for the treatment of exhaust gases.

It will be appreciated that the types of scrubbers used include standard emission scrubbers, also known as wet scrubbers, with the invention applicable to any such suitable scrubber.

The ballast water treatment 155 is accomplished by using filtration, electro- disinfection and neutralization of the residual oxidant. The schematic diagram of the process 155 is shown in Figure 3.

The first unit in the treatment is filtration 165. The filtration by using one or two self-cleaning micro-strainers 190 during the intake process from an inflow 160 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 can effectively remove various bio-solids (colloidal substances), which can lead to formation of disinfection byproducts (DBPs) in the presence of chlorine. With the filtration system 190 the amount of disinfectants required will be reduced and the concentrations of DBPs can also be reduced.

The disinfectants are generated by the electrolysis of the salt water in the electrolytic cell(s) 215. The total residual oxidant (TRO) is measure by a TRO analyzer 175, 230 and controlled at a pre-set value through a computer 182. One or few rectifiers 220 with one or few chillers 225 may be used. A control computer 182, TRO analyzers 175, 230 for measuring total residual oxidants (TRO), and flow transmitters will be used. As seawater is corrosive, corrosion-proof materials will be used for the construction of the reactor.

Before de-ballasting 185, a neutralization solution (sodium thiosulfate, Na₂S₂O₃) is injected 177 prior to ballast water pump 170 to react with 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:

[Na₂S₂O₃] (mg/L) = [total residual oxidant (as chlorine)] x factor

The concentration of total residual oxidants (mg/L, as chlorine) is determined by the TRO analyzer 175, which provides real-time measurement of TRO concentration. The factor is 0.65 - 0.75. The neutralization system 180 is composed of chemical storage vessel, metering pump for chemical inject, and the computer 182.

Ballasting Process: Valves 183, 243, 192, and 208 are closed. Valves 169, 179 & 212 are opened. The water (which may be sea water or fresh water, depending on the application) goes through strainer 165, valve 169, ballast water pump 170, valve 179, self-cleaning micro-strainer 190, electrochemical disinfection unit 205 and valve 212 in series, and then fills in the ballast tanks 240. Ventilation 235 (optional) is turned on so that the hydrogen gas and/or 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 169, 179 & 212 are closed. Subject to the selected process, either one of the outflow Valves 183 or 192 or 208 are opened, together with valve 243. Valve 192 or 208 may be opened so that the water is filtrated 190 or disinfected 205 again prior to de-ballasting.

The water is pumped from the ballast tanks 240, and goes through valve 243, pump

170, and valve 183 (or 192 or 208) in series, and then is discharged 185 (or 195 or 210).

Before the pump 170, neutralization solution is injected 177 to remove the total residual oxidant (such as chlorine) to below 0.1 mg/L. The neutralization concentration is determined by the above equation. When Valve 183 is opened and Valve 192 and 208 are closed, the water is released 185 to the water environment (e.g. sea, lake, canal etc) without filtration and disinfection. However, two options are provided. When Valve 192 is opened and both Valves 183 and 208 are closed, the water is filtrated 190 and discharged 195. When Valve 208 is opened and Valve 183 and 192 are closed, the water is filtrated 190, disinfected 205 and discharged 210.

Table 3 Theoretical calculation of Cl₂ and NaOH consumption in exhaust gas treatment

For a typical 5000TEU container ship, the power of the engine is 50,000 kW. It gives the amount of CO₂, SO_x, and NO_x are shown in Table 4.

Table 4 Estimated amount of gaseous species in exhaust gases from a 5000TEU Ship

In order to remove 100% SO₂ and 100% NO_x (assumed NO), the theoretical

NaOH and Cl₂ consumption are 787.5 kg and 2,010 kg, respectively, based on Table 3.

It was found through experiments that the system given in Figure 1 that the generation of 2010 kg Cl₂ can lead to a production of 3,522 kg NaOH. The amount of NaOH after the reaction between NaOH and SO₂ will be 2734.5 kg (3,522-787.5=2734.5 kg), which may be employed to remove NO₂ and CO₂.

SO₂ is much easier to be dissolved in seawater and alkaline solution than NO_x and CO₂. If the removal of NO_x and CO₂ is not considered, we only need 787.5 kg NaOH, which requires energy of 2700 kW or 5% of power of the engine (50,000 kW).

The advantages are: 1. Heavy fuel with lower cost can still be used and 2. The size of scrubbers can be greatly reduced. In further embodiments:

1) A consumption of electrolytic cell comprises a membrane that separate the cell to an anode compartment and a cathode compartment, which produces Cl₂ and NaOH respectively. The streams from the two compartments 10, 15 can be merged to produce OCl^" and HOCl.

2) The above described system can be used for fresh water situation with an addition of salt to Inlet 30 and 35 of Figure 1. It will be appreciated that whilst NaCl is the common salt used in such a process, processes that rely on KCl, CaCl₂ and MgCl₂ may also be used.

Experimental Data

Our bench- and pilot-scale studies with TRO of 3 to 12 mg/1 (of Cl₂) have confirmed that the IMO regulated microorganisms can be fully killed with an extremely low energy consumption of approximately 0.006 kwh/m³. The pH after such an operation is unchanged and maintained at pH 7.5 to 8.5.

The electrodes (metals from the Pt group and their metal oxides, such as Ti coated with Ru and/or Ir oxides) are used in order to effectively produce disinfectants and to avoid serious corrosion problems. They have advantages of higher production of chlorine and free radicals with lower energy consumption, and higher resistance to corrosion. RuO_n,, Ti, IrO_n, and Pt are recommended. MnO_x electrode will produce no oxygen; it may be used if chlorine is not wanted. The disinfectant with such a concentration should not become concerned, as it can go through rapid decay (around 1 day) and the corrosion under such a condition is similar to that when the disinfectant is not present, which was confirmed experimentally (Table 5). The effect of operation on the corrosion of ballast tank is insignificant.

Table 5 Effect of electro-disinfection on corrosion in ballast tank

In addition, , corrosion and bio-corrosion in the ballast tank may be avoided due to the presence and effect of chlorine in the water.

The seawater after the above disinfection will stay in the ballast tank throughout the whole journey. When the ship reaches the next port, the ballast water will be released. A series of measurements of disinfectant byproducts, modeling studies and eco-toxicity studies have confirmed that the discharged treated ballast water has an insignificant toxicity to the marine environment. The technology is safe for use.

Claims

1. A treatment system comprising

an electrolytic cell, having an anode compartment and a cathode compartment, said electrolytic cell having an inlet for receiving salt water, said cell arranged to produce an alkaline solution within the cathode compartment and a disinfecting solution within the anode compartment;

an alkaline scrubber unit for the treatment of exhaust emissions from a ship- mounted engine, said alkaline scrubber unit for receiving the alkaline solution and the exhaust emissions into a first chamber for mixing the exhaust emissions and alkaline solution mix, and;

a disinfection unit intermediate a water inflow and a ballast tank, said disinfection unit arranged to receive the disinfecting solution and water from the water inflow so as to disinfect said water before delivery to the ballast tank.

2. The treatment system according to claim 1, wherein electrolytic cell includes a central compartment divided by a membrane so as to isolate the anode and cathode into the anode and cathode compartments.

3. The treatment system according to claim 1 or 2, further including a chlorinated scrubber unit for receiving chlorinated salt water from the anode compartment and the exhaust emissions into a second chamber for mixing the exhaust emissions and chlorinated salt water, said chlorinated scrubber unit including an outlet for delivering the remaining exhaust emissions to the chamber of the alkaline scrubber unit.

4. The treatment system according to any one of claims 1 to 3, further including a water scrubber unit for receiving water and remaining exhaust emissions from the alkaline scrubber unit into a third chamber for mixing the remaining exhaust emissions and water, said water scrubber unit including an outlet for discharging the treated liquid.

5. The treatment system according to any one of claims 1 to 4, wherein the disinfection unit is arranged to receive discharge water from the ballast tank for disinfecting said discharge water before delivery to a ballast tank outflow.

6. The treatment system according to any one of claims 1 to 5, wherein the disinfecting solution is chlorinated salt water from the anode chamber.

7. The treatment system according to any one of claims 1 to 5, wherein the disinfecting solution is sodium hypochlorite salt water formed from mixing chlorinated salt water from the anode chamber with the alkaline solution from the cathode chamber.

8. The treatment system according to any one of claims 1 to 7, further including a neutralization system, said neutralization system including an analyzer for determining a total residual oxidant of water from the water inflow and a control system for instructing an injector to inject neutralizing solution into the water, based on the determined total residual oxidant.

9. The treatment system according to any one of claims 1 to 8, wherein treatment of the exhaust emissions includes dissolution of any one or a combination of: SO_x, CO₂ and NO_x.

10. The treatment system according to any one of the preceding claims, further including a mixing zone arranged to receive fresh water and into which salt is added so as to provide the salt water at a pre-determined concentration.

11. The treatment system according to any one of the preceding claims, wherein the electrolytic cell includes an array of electrolytic cells, the array arranged to deliver alkaline solution from respective cathodes to the first chamber and disinfecting solution from the respective anodes to the disinfection unit.

12. A method of treatment, said method comprising the steps of:

delivering salt water to an anode and cathode;

electrolyzing the salt water and so producing a disinfecting solution at the anode and an alkaline solution at the cathode;

delivering exhaust emissions from a ship-mounted engine and said alkaline solution to a first chamber;

treating said exhaust emissions by mixing with the alkaline solution within said first chamber;

delivering water from an inflow and the disinfecting solution to a disinfection unit, and; treating said water by mixing with the disinfecting solution within said disinfecting unit.

13. The method according to claim 12, further including, before the delivering step to the first chamber, the steps of:

delivering chlorinated salt water from the anode compartment and the exhaust emissions into a second chamber;

treating said exhaust emissions by mixing with the chlorinated salt water;

delivering remaining exhaust emissions to the first chamber.

14. The method according to claim 12 or 13, further including, after the treating step in the first chamber, the steps of:

delivering remaining exhaust emissions from the first chamber into a third chamber; delivering water to said third chamber;

treating said remaining exhaust emissions by mixing with the water;

discharging the treated liquid.

15. The method according to any one of claims 12 to 14, further including the step of delivering said treated water from the disinfection unit to a ballast tank.

16. The method according to any one of claims 12 to 15, further including the steps of: analyzing the water prior to the treating step;

determining a required quantity of neutralizing solution to add to the water to reduce total residual oxidants, and; injecting said required concentration into the water.

17. The method according to any one of claims 12 to 16, further including the step of reversing polarity of electrodes within the electrolytic cell for a pre- determined period, so as to remove scale from said electrodes.