Technical field The invention relates to an on-board system and method for the treatment of ballast water on ships. The system and method are designed to kill living organisms in the ballast water, which could be harmful if released into the surrounding environment. Specifically, the invention relates to a hybrid treatment system and method comprising ballast water exchange and chlorination.

Background

Ballast water is taken into tanks on most ships to adjusting the buoyancy of the ship. The buoyancy of a ship in turn depends on the weight of the ship and the weight of the cargo it is carrying. Large tankers and bulk cargo carriers use a tremendous amount of ballast water, which is often taken on in the coastal waters in one region after such vessels unload cargo or discharge wastewater. Such ballast water is then discharged at the next port of call when more cargo is loaded. Ballast water discharge typically contains a variety of biological materials, including plants, animals, viruses and other microorganisms. These biological materials often include non-native, nuisance, and exotic species commonly referred to as Aquatic Invasive Species ("AIS"), which can cause extensive ecological, environmental, and economic damage to aquatic ecosystems. Examples of such damage include the zebra mussel invasion in the Great Lakes, and the Asian clam invasion in U.S. aquatic ecosystems.

A ballast system typically comprises (1) a sea water inlet into the vessel that provides a source of water to fill the ballast tanks, (2) a pump to fill and empty ballast water tanks, (3) a piping system and valves to convey and remove ballast water to/from individual tanks within the vessel, and (4) an overboard discharge to pump ballast water overboard. It is well known in the art to perform ballast water exchanges in the open ocean in order to avoid the introduction of AIS into new ecosystems. There are three methods for conducting ballast water exchange. These are (1) sequential method, (2) flow-through method, and (3) dilution method.

In the sequential method, the ballast tanks are first emptied and then refilled with replacement ballast water. Particular disadvantages of the sequential method are that it can significantly decrease the stability of the ship (because the ballast tanks are emptied at sea) and it can generate large stresses on the hull girder of the ship.

In the flow-through method, replacement ballast water is pumped into the bottom of a full ballast tank causing existing ballast water to flow out through an overflow. To complete an exchange, the amount of water brought through the ballast tanks is typically about three (3) times the volume of the ballast tank.

The dilution method is similar to the flow-through method in that about three times the volume of the ballast tank is used, but in the dilution method, replacement ballast water is pumped into the top of full ballast tank with existing ballast water being simultaneously discharged from the bottom of the ballast tank.

Both the flow-through method and the dilution method avoid the decrease in stability and the increase in hull stress that are generated when the sequential method is used. All three of the above methods utilize standard pumping systems to perform the ballast water exchange.

However, using ballast water exchange as the sole method of preventing the spread of AIS has a number of shortcomings. Firstly, it is not always safe to perform ballast water exchange, for example due to poor weather or sea surface conditions. Secondly, the sequential method may lead to a decrease in stability of the ship because the ballast tanks are emptied, which significantly increases the buoyancy of the ship, prior to the refilling of the ballast tanks. Thirdly, ballast water exchange is not completely effective since: (1) some AIS still remain in the ballast tank after ballast water exchange has occurred, and (2) some AIS are resilient to high saline conditions and may subsequently be discharged at the next port after being taken on-board a vessel's ballast tanks during ballasting.

In order to mitigate transfers of AIS between geographical areas of the world, governmental authorities governing international marine shipping have mandated:

As a temporary measure, that ballast water be exchanged at sea. The dosing of water ballast tanks with clean ocean ballast water has been seen to significantly reduce the amount of AIS transferred between geographical areas in ballast water; and

As a permanent measure and to replace ballast water exchange, the International Maritime Organization (the "IMO") has mandated that vessels be fitted with approved ballast water treatment systems (subject to the international convention being ratified). The IMO approval process requires that a ballast water treatment system be shown to be effective at enminating (killing) AIS according to set prescriptive criteria. Ballast water treatment systems are also known in the art. There are presently approximately 25 IMO approved ballast water treatment systems commercially available to replace ballast water exchange, and about as many under development. For example, Hyundai has developed a system called HlBallast™, which comprises a filter, an electrolysis unit and a neutralization unit. The electrolysis unit produces chlorine as a disinfectant to kill AIS. However, the system has several disadvantages, including: the costs associated with purchasing and installing such a system; that the system requires the addition of salt to treat fresh water as the process to make chlorine on-board the vessel involves electrolysis; and that hydrogen gas formed during the electrolysis needs to be vented safely, etc. Other known systems have similar types and varieties of disadvantages.

In order to overcome these disadvantages, what is needed is a system which combines the advantages provided naturally by nature through the ballast water exchange with ballast water treatment to effectively prevent the spread of AIS, rather than simply replacing the ballast water exchange system with a ballast water treatment system.

Summary of the Invention The present invention serves to implement a hybrid water ballast treatment system in shipping vessels that meets the standards required by IMO for the effective eUmination of AIS. The hybrid water ballast treatment system combines a ballast water exchange system with a ballast water treatment system, to reduce the spread of AIS.

The present invention described herein serves to eliminate and kill AIS and reduce their spread by continuing to perform the ballast water exchange as per established practice but at the same time, augmenting the kill rate of AIS by adding metered amounts of disinfectant to the exchanged ballast water. Preferably, the disinfectant is chlorine in the form of industrial strength sodium hypochlorite (NaOCl).

The ballast water is dosed with up to 10 ppm chlorine to achieve an effective kill rate of AIS. During the rest time of the chlorine in the ballast tanks, the chlorine will decay depending on the organic load contained within the ballast water. A by- product of dosing ballast water with chlorine is the formation of trihalomethanes. The amount of trihalomethane formation is a function of the chlorine dosage amount and the organic load. In many jurisdictions, the discharge of trihalomethanes is strictly controlled by law, so care and attention are required to stay within regulatory discharge limits. Similar attention must be paid to the discharge of chlorine, which is also subject to regulatory limits. If residual chlorine amounts exceed regulatory limits, then the ballast water must be dechlor nated before discharge by adding sodium thiosulphate to the ballast water, for example. The present invention serves to supplement the typical ballast system by adding disinfectant dosage pumps and piping to inject metered amounts of disinfectant to augment the kill rate of AIS in the water used to fill ballast water tanks. The dosed amount of disinfectant is injected utilizing a metering pump into the ballast piping and / or close to the bell mouth in each ballast tank in such a manner that disinfectant is mixed into the ballast water stream mcoming to each ballast tank.

The addition of the process of injecting metered amounts of disinfectant to the ballast water on marine vessels shall increase the kill rate of AIS in typical ballast water exchange systems to meet equivalent standards prescribed by such international regulatory organizations such as the IMO.

The advantages of the hybrid ballast water treatment system include significantly improving the kill rate of AIS, in particular of enterococcus, coliforms, Escherichia coli ("E. coli"), algae, chlorophyll, etc. The benefit of the hybrid ballast water treatment system is the synergistic interaction effect of the two treatments (ballast water exchange plus disinfectant), as detailed below.

The hybrid system can be easily retro-fitted into pre-existing ships, which is a much simpler task than installing another type of ballast water treatment system. The estimated cost of installing the hybrid ballast water treatment system is between 1/10 and 1/4 the cost of installing other approved systems because most of the AIS killing is performed by nature through the mid-ocean clean water ballast exchange rather than using engineering and chemical treatment systems to remove AIS.

According to a first broad aspect the invention seeks to provide a system for reducing the amount of aquatic invasive species ("AIS") in ballast water, the system comprising: a ballast water treatment system; and a ballast water exchange system. According to a second broad aspect the invention seeks to provide a method for reducing the amount of aquatic invasive species ("AIS") in ballast water, the method comprising the steps of: treating the ballast water; and performing ballast water exchange of said treated ballast water. Brief Description of the Figures

Figure 1 is a schematic of a ballast system of the prior art;

Figure 2 is a schematic of a first embodiment of the hybrid ballast water treatment system;

Figure 3 is a schematic of a second embodiment of the hybrid ballast water treatment system; and

Figure 4 is a flow chart describing a method of hybrid ballast water treatment system. Detailed Description

Throughout Figures 1 to 3, a blackened triangle (A) indicates the direction of ballast water flow. Referring to Figure 1, a ballast system (1) of the prior art is shown. The ballast system (1) comprises a ballast pump (3), a ballast tank (5), intake piping (7), and discharge piping (9). Intake piping (7) and discharge piping (9) each contain valves (not shown) to control the flow of ballast water. The placement and type of valve used would be within the knowledge of a person of skill in the art. When the cargo of a ship has been unloaded at a first port, an intake of ballast water is needed to compensate the buoyancy of the ship. Coastal water is drawn into the ship through ballast water inlet (2) by ballast pump (3) through intake piping (7) and into ballast tank (5). With the ship's buoyancy compensated, the ship is able to set sail for a second port. Prior to, or during the loading of cargo at the second port, ballast water is discharged from ballast tank (5) through discharge piping (9) and out through ballast water outlet (8) to compensate for the weight of the cargo. The ballast water (from the first port) discharged into the second port may contain aquatic invasive species ("AIS") which could harm or render local aquatic species extinct.

Referring to Figure 2, a first embodiment of a hybrid ballast water treatment system (10) is shown. The hybrid ballast water treatment system (10) comprises at least one ballast pump (3), at least one ballast tank (5) (two are shown by way of example), intake piping (7), and discharge piping (9). The piping may be arranged so that a portion of the piping serves both as intake piping (7) and discharge piping (9). The system further comprises a disinfectant storage tank (20) for storing disinfectant, a metering pump (40) for providing measured dosages of a disinfectant, disinfectant tubing (60), and a measurement meter (80) for measuring the concentration of disinfectant in the ballast water. Preferably, the disinfectant is chlorine, provided from industrial strength sodium hypochlorite (i.e. bleach), which is readily available and accessible. Other disinfectants would be known to a person of skill in the art, for example peroxide, ozone, etc. Preferably, the metering pump (40) is a peristaltic pump. However, any type of pump known to a person of skill in the art and capable of delivering measured doses of a disinfectant could be used. In this embodiment, the disinfectant tubing (60) is connected at its first end to the disinfectant storage tank (20), passes through the metering pump (40) and is connected at its second end to intake piping (7) in order to improve mixing of the disinfectant with the ballast water and uniformity of disinfectant distribution. While Figure 2 shows the second end of disinfectant tubing (60) joining intake piping (7) prior to ballast pump (3), the second end of disinfectant tubing (60) could also be joined to intake piping (7) subsequent to ballast pump (3). Additionally, disinfectant piping (60) contains valves (not shown) to control the flow of disinfectant into intake piping (7), ballast tank (5), and discharge piping (9). The placement and type of valve would be within the knowledge of a person of skill in the art. However, gate valves, ball valves or butterfly valves are preferably used.

Preferably, a measurement meter (80) is connected to at least one of disinfectant piping (60) and discharge piping (9) to measure the amount of disinfectant. In instances where the hybrid ballast water treatment system (10) uses chlorine as a disinfectant, the hybrid ballast water treatment system may additionally contain at least one sodium sulfate (Na ₂ S ₂ 03) storage tank (22). The sodium sulfate is used to dechlorinate ballast water being discharged from discharge piping (9) having a chlorine concentration that exceed discharge regulatory limits. The sodium sulfate tank may be connected to a metering pump (40), which draws sodium sulfate from sodium sulfate tank (22) and into discharge piping (9).

Referring to Figure 3, a second embodiment of the hybrid ballast water treatment system (15) is shown. This embodiment is similar to the embodiment shown in Figure 2. However, instead of the disinfectant tubing (60) being connected at its second end to intake piping (7), it is connected directly to the ballast tank (5) in proximity of the ballast tank (5) fill or discharge point. Referring to Figure 4, an exemplary method of using hybrid ballast water treatment system (10) or (15) is shown. While at a first (load) port, the disinfectant storage tank (20) is filled with disinfectant (step 100). As the ship nears its destination (discharge port), ballast water exchange is performed (step 200a). The ballast water exchange method may comprise the sequential method, the flow- through method, or the dilution method. Simultaneously with step 200a, a disinfectant is pumped (step 200b) using metering pump (40) from disinfectant storage tank (20) through disinfectant tubing (60) into at least one of intake piping (7), ballast tank (5), and discharge piping (9). Preferably, the disinfectant is chlorine, added at up to ten (10) parts per million to the ballast water. After the ballast water exchange (step 200a) and chlorination (step 200b) processes have been completed, the ship can arrive at the discharge port (step 300). The addition of a disinfectant to the ballast water when used in combination with ballast water exchanges improves the killing rate of AIS because the disinfectant kills AIS that may not be killed by the high salinity of the open-ocean salt water.

A person of skill in the art would recognize that the number and positioning of ballast tanks (5), disinfectant storage tanks (20), metering pumps (40), dosage meters (80), and sodium sulfate storage tanks (22) could be varied without affecting the working of the invention.

Experiments Methodology Three (3) voyages of the Federal Venture ("FV") were taken in which three

Experiments were performed to determine the effectiveness of combining chlorination and ballast water exchange on AIS.

The FV has a total of ten ballast tanks. Four different treatments were performed (i.e. control, ballast water exchange only, chlorination only, ballast exchange and chlorination). For Experiments 1 and 2, the ten ballast tanks were split up as follows: two tanks were used as controls; two tanks were used for chlorination only; three tanks were used for ballast water exchange ("BWE") only; and three tanks were used for combined chlorination and BWE. For Experiment 3, the number of ballast tanks performing control and chlorination replicates was increased from two to three with the remaining two treatments having two replicates each. None of the ballast tanks used for chlorination were ever used for non-chlorinated treatments. Of the three voyages, voyages 1 and 3 departed from Port-Alfred,

Saguenay, Quebec, Canada, and voyage 2 departed from Trois Rivieres, Quebec, Canada. The destination of voyage 1 was Sao Luis, Brazil. The destination of voyages 2 and 3 was Vila do Conde, Brazil. In each case, the Experiment started with the refilling of ballast tanks at port, delivery of the first doses of chlorine (to treatments requiring it), and initial sampling in the engine room. These processes were carried out simultaneously, in the sequence shown below in Table 1. Ballasting at port was carried out over the course of one to three days using two ballast pumps with a total capacity of 800 m ³ hour ¹ . The sequence of filling of ballast tanks was carried out according to the ship's normal filling and discharge regime. Between days four and five after departing port, ballast water exchange was initiated together with a second dosing of chlorine on tanks 2, 3F, and 3A (Experiments 1 and 2; see Table 1), or 3F, and 3 A (Experiment 3). In other words, whenever chlorine was added to tanks, ballast water also was being added simultaneously (which help thoroughly mix the former). Open sea BWE was carried out over seven to twelve hours in order to facilitate exchange of three times the ballast tank volume (i.e. approximately 95% volumetric exchange, in compliance with IMO requirements). During this procedure, the engine was stopped and the ship drifted no more than 15 nautical miles from the original position. Sampling of exchanged marine water was carried out during the BWE operation in the engine room during the third trip. Final samples were collected approximately two days following BWE; these samples and measures of environmental conditions of the ballast water were taken from water pumped to the forecastle. Environmental conditions of ballast water were measured in - the engine room and forecastle for initial and final samples, respectively; environmental conditions were measured at the location where samples were taken. On both occasions, variables were measured with the same equipment and methodology. Samples for zooplankton, phytoplankton and bacteria analysis were collected and processed on board. When necessary, samples for bacteria were diluted using distilled water from the GLIER (University of Windsor). Samples for bacteria were incubated for 24-48 hours and the number of positive cells counted used to estimate to the most probable number of colony-forming units ("CFU"). Fresh and fixed samples for zooplankton and phytoplankton were processed on board under dissecting and epifluorescence microscopy, respectively.

All abundances were transformed using a log(x+l) function, where x was the initial or final density of live organisms, to satisfy statistical requirements. Statistical differences on the ratio final/ Initial densities of log transformed data were analyzed using a two-way ANOVA (treatments of chlorine and ballast exchange, and their interaction).

Environmental Conditions

Factors were identified, which introduce environmental and biological variation between ballast tanks at the beginning of the experiment, and have to consider them for the analysis of the final results. Total time spent ballasting and refilling tanks (without interruptions) were important factors affecting initial conditions in all tanks. For example, shorter ballasting time on the last experiment as compared to the first two resulted in similar measures of environmental variables in all treatments at time 0 (Table 1). However, other factors including tidal flow and freshwater flowing in from the nearby Mars River at Port- Alfred, or local daily variability at Trois Rivieres, introduced variability between consecutively refilled tanks. Table 1: Schedule of the three experiments on board of the Federal Venture. P & S denote port and starboard tanks respectively.

Tank Starting Ending Latitude Longitude Capacity

(Date/Time) Date/Time) M

Experiment 1: ballasting at port, first dosing of chorine and initial sampling

Tank 1 F 4/14/12 4/14/12 48°20'6.86"N 70°52'13.67"W 1016.4x2 (P* & S) 10:29 11 :42

Tank 1 A 4/14/12 4/15/12 48°20'6.86"N 70 ^o 52'13.67"W 1287.5x2 (P* & S) 16:43 16:09

Tank 2 (P* 4/1.5/12 4/15/12 48°20'6.86"N 70°52'13.67"W 1276.4 x2 & S) 21:05 22:40

Tank 3 F 4/13/12 4/13/12 48°20'6.86"N 70 ^o 52'13.67"W 1021.2 x2 (P* & S) 20:46 22:55

Tank 3 A 4/14/12 4/14/12 48°20'6.86"N 70°52'13.67"W 1091.2 x2 (P* & S) 14:14 15:28

Experiment 1: BWE and second dosing

Tank 2 (P* 4/19/12 6:45 4/19/12 40°48'46.1"N 62°36'12.2"W 1276.4 x2 & S) 11 :29

Tank 3 F 4/19/12 4/19/12 40°5Γ49.8"Ν 62°35'01.3"W 1021.2 x2 (P* & S) 11:55 15:59

Tank 3 A 4/19/12 4/19/12 40°45'00.6"N 62°34'27.6"W 1091.2x2 (P* & S) 16:27 20:35

Experiment 2: ballasting at port, first dosing of chlorine and initial sampling

Tank 1 F 7/04/12 7/04/12 46°19'55.87"N 72°32'40.96"W 1016.4 x2 (P* & S) 07:38 10:29

Tank 1 A 7/03/12 7/03/12 46 ⁰ 19'55.87 ^Μ Ν 72°32'40.96"W 1287.5 x2 (P* & S) 10:26 16:43

Tank 2 (P* 7/04/12 7/04/12 46 ⁰ 19'55.87"N 72°32'40.96"W 1276.4 x2 & S) 13:40 21:05

Tank 3 F 7/05/12 7/05/12 46°19'55.87"N 72°32'40.96"W 1021.2 x2 (P* & S) 11:00 20:46

Tank 3 A 7/05/12 7/05/12 46°19'55.87"N 72 ^o 32'40.96"W 1091.2x2 (P* & S) 00:22 14:14

Experiment 2: BWE and second dosing

Tank 2 (P* 7/10/12 7/10/12 33°28'32.26"N 54o40'06.48"W 1276.4 x2

& S) 16:45 21 :30

Tank 3 F 7/10/12 7/10/12 33°29'13.52"N 54o 1 021 .2x2

44'46.27"W

(P* & S) 12:11 16:30

Tank 3 A 7/10/12 7/10/12 33°31 '03.42"N 54°47'47.78"W 1 091 .2x2 (P* & S} 10:00 12:00

Experiment 3: ballasting at port, first dosing of chlorine and initial sampling

Tank 1 F 9/17/12 9/17/12 48°20Ό4.46"Ν 70°52'23.89"W 1016.4x2 (P* & S) 03:23 04:45

Tank 1 A 9/17/12 9/17/12 48°20'04.46"N 70°52'23.89"W 1287.5x2 (P* & S) 06:00 07:30

Tank 2 (P* 9/17/12 9/17/12 48°20Ό4.46"Ν 70°52'23.89"W 1276.4x2 & S) 00:44 02:45

Tank 3 F 9/16/12 9/16/12 48°20Ό4.46"Ν 70°52'23.89"W 1021.2x2 (P* & S) 21:05 22:30

Tank 3 A 9/17/12 9/17/12 48°20O4.46 ^U N 70°52'23.89"W 1091.2x2 (P* & S) 21:31 22:40 Tiiird trip: BWE and second dosing

Tank 3 F 09/23/12 09/23/12 37° 0'20.32"N 55°42'18.38"W 1021.2x2

(P* & S) 08:00 08:00

Tank 3 A 09/23/12 09/23/12 36°49'5.76"N 55 ^o 30'36.50"W 1091.2x2

(P* & S} 08:00 08:00

Asterisks indicate tanks dosed with chlorine. Geographic coordinates of ballast water exchange on the ocean are provided.

Initial temperature values at Port-Alfred were lower relative to those at Trois Rivieres, however final values were similar in all trips. Ballast water temperature increased in all three experiments, but particularly so in Experiments 1 and 3, which were conducted earlier and later in the year, respectively, when port waters were <10 °C. Final water temperature in Experiment 1 ballast tanks was 20 °C, whereas in Experiments 2 and 3, it was 27 °C.

Most of the variation in pH was associated with BWE, which increased pH from 7-7.5 to almost 8.0. Additionally, very high pH values were recorded in treatments involving both BWE and chlorine dosing hybrid treatment. Overall, pH increased in Experiments land 2in ballast tanks that conducted BWE, whereas it decreased in control, chlorine only, and BWE treatments in Experiment 3.

Oxygen concentration was typically lower at Port Alfred (Experiments 1 and 3) as compared to Trois Rivieres. Overall, oxygen concentration of BWE decreased in treatments with BWE in Experiment 1, but increased in Experiment 2 in all tanks except those with BWE alone. In Experiment 3, oxygen concentration was low in all tanks initially, though it increased in all treatments in final assessments, particularly those involving BWE. The initial salinity of ballast water was higher in Port-Alfred than at Trois Rivieres. These differences in salinity were associated with a tide effect in combination with freshwater incoming from a nearby river. Trois Rivieres displayed salinity values close to zero due to the location of the port on the Saint Lawrence River, far away enough from tide influence. Overall, salinity was, as expected, higher in all experiment in treatments that involved open ocean BWE. In addition, salinity values increased from initial to final concentration across all treatments in Experiment 3. Results

In general, the hybrid (BWE and chlorine) and chlorine treatments had the lowest final values among all treatments for Enterococcus, conforms, and £. coli. For these two treatments, the final densities of these three bacterial indicators were lower than the prescribed IMO limits (see Table 2, below). For Enterococcus and E. coli bacteria, the hybrid treatment had a significant or marginally significant synergistic effect, respectively (p = 0.02 and 0.08, respectively) with high test power (0.64 and 0.41, respectively). Control and particularly BWE treatments displayed the highest final abundances. Chlorination alone had densities intermediate to those in control and hybrid treatments. With both bacterial indicators, the BWE treatment only experienced increased abundances in final population abundances. Increasing bacteria densities were probably related to two environmental factors: higher final temperatures and good oxygen conditions in the ballast tanks. Also, concentrations of bacteria in the marine water, which was pumped into ballast tanks, was higher than that observed at the initial time in port. Results for E. coli bacteria largely parallel those of the other two indicators. Experiments began with slightly higher abundances in tanks designated for BWE or the hybrid treatments. Final densities of E. coli were highest in the BWE-only treatment, lower in controls, and lowest in the chlorine-only and hybrid treatments. Overall, application of chlorine dramatically reduced all bacterial indicators used, though results were the same or better in the hybrid.

Experiment 3

Enterococcus ¹ 51.1 ± 0.0 ±0.0 2107.5 ± 0.3 ±0.1 <100

49.0 32.9

coliforms ¹ 8371.2 ± 0.0 ±0.0 635.9 ± 0.0 ± 0.0 <10

967.2 95.0

Escherichia 0.0 ±0.0 0.0 ±0.0 15.8 ± 1.6 0.0 ±0.0 < 250 coli '

Vibrio cholera ⁴ - - - - <1

Algae ² 15.6 ± 14.3 1.7 ± 1.92 0.6 ±0.1 0.6±0.1 <10

Chlorophyll ³ 0.57 ±0.01 0.47 ±0.04 0.45 ± 0.07 0.36 ± 0.03 -

Zooplankton ⁵ 8.0 ± 12.01 0.0 ±0.0 45.0 ± 33.29 0.0 ± 0.0 < 10

Average of Experiments 1-3

Enterococcus ¹ 330.8 ± 25.3 ± 56.6 611.9±911.7 0.72 ± 1.3 < 100

581.4

coliforms ¹ 3942.4 ± 0.2 ±0.53 1292.8 ± 0.04 ± 0.2 <10

4532.8 907.1

Escherichia 2.6 ± 3.9 0±0 57.01 ± 0±0 < 250 coli ' 134.31

Vibrio cholera ⁴ - - - - <1

Algae ² 2162.2 ± 8.38 ± 160.7 ±243.0 4.83 ±8.7 <10

4044.5 16.75

Chlorophyl 0.7 ±0.5 0.44 ± 0.22 0.5 ±0.3 0.27 ±0.1 -

Zooplankton ⁵ 204.8 ± 1616.6 ± 334.6 ±455.1 33.3 ± 87.9 <10

525.9 2764.3

¹ colony-forming unit per 100 ml (CFU);

² cells (> 10 μπι and < 50 μη) per ml;

³ μιη of chlorophyll per litter;

⁴ Analysis to be completed;

⁵ organisms (>50 μιη) per m ³ Initial density of phytoplankton sized organisms were similar in all four treatments. Treatments diverged in final abundances. The lowest average values of microplankton density were observed in the hybrid treatment, in which the application of BWE and chlorine resulted in a significant interaction (p = 0.02; test power =0.64). This trend was similar regardless of the wide range of initial concentrations of organisms in the three experiments. In Experiment 3, in which the total initial density of microplankton (phytoplankton) was the lowest among all experiments, and all treatments displayed final value lower than the IMO D-2 standard, the hybrid treatment displayed the best performance.

The chlorophyll concentration displayed, in general, a similar trend to microplankton density, with similar starting conditions in different treatments (slightly higher concentration in BWE and hybrid treatments). Chlorophyll concentration was lowest, overall, in the hybrid treatment, however the power test was not as high as with microplankton (0.046), illustrating the value of direct counting of organisms under epifluorescence microscopy.

Zooplankton results are limited to two experiments due to destruction of samples shipped with FedEx™ from Iceland following the first Experiment. In general, populations of zooplankton had similar initial densities in both Experiments. Overall final density was highest in the control treatment, followed by BWE, chlorine, and, finally, the hybrid treatment. Final densities during second trip illustrated that none of the treatments was under the IMO D-2 standard of 10 organisms/ m ³ . Nevertheless, the hybrid BWE and chlorination treatment was lowest with a final density of 56 organisms/ m ³ . During the third experiment, the initial density was very low, and therefore, significant differences between BWE and the hybrid BWE and chlorination treatments could not be assessed. The decline in density during third experiment was most evident in treatments that included chlorine. Therefore, the hybrid BWE and chlorination treatment appears to offer the best protection in terms of reduction in viable populations of zooplankton. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.