The introduction of steel-hulled vessels, lead to the use of water ballast system where water is pumped in to the vessel to decrease the stresses occurring on the hull, while providing transverse stability and improving propulsion and maneuverability [3]. It also, compensates for weight shifts in different cargo load level operation, thus water ballast ensures the safe and efficient operation of the vessel. However, due to the fact, that marine species, i.e. bacteria, microbes, small invertebrates, eggs, cysts and large various species are getting pumped during the filling process of water ballast [3]. Consequently, creating several problems, such as ecological, health and economic ones.

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1.2 BWM standard requirements

IMO has implemented the following two BWM standards D-1, D-2. D-1 standard requires ship to discharge their ballast water in deep water (200 meters deep) and at distance 200 nautical miles away from land, by doing that it decreases the chances of organisms surviving in the deep-sea water environment. D-2 standard relates to the size of discharged organism, as follows [3]:

Less than $10$
viable organisms per $m^{3}$
, which are greater than or equal to $50 mm$
in minimum dimensions.
Less than $10$
viable organisms per $mL$
, which are in size of $10 - 50 mm$
in minimum dimensions.
Less than $1$
colony-forming unit (cfu) per $100 mL$
of toxicogenic vibrio cholerae.
Less than $250 cfu$
per $100 mL$
of Escherichia coli.
Less than $100 cfu$
per 100 mL of Intestinal Enterococci.

The current status of BWM conventions is showed on figure 1, which shows, when new and existing ships need to comply with D-1 and D-2 conventions and the requirement of having a BWM plan, ballast water record book and the BWTS to be certified by the IMO.

2. IMO approved BWM systems

2.1 Ecochlor BWTS

2.1.1 Working Principle

The Ecochlor BWTS is a chemical solution, which consists of a filtration process and a Chlorine Dioxide ( $Cl O_{2}$

) treatment system to remove smaller organisms.

2.1.2 Process Description

The first step of the BWTS is the filtration system (Figure 2), where the filter mechanism prevents larger objects from entering the inlet chamber. Moving on to the next stage of the filter mechanism is the premilitary process for flushing, where the water goes into a “cake” sediment (Coarse screen) [2]. At this section, variable pressures are applied, depending on the thickness of the sediment, until it reaches the desired pressure (usually 0.5 bar) to initiate the flushing process [2]. The Second stage is the $Cl O_{2}$

supply at the injection point to the water ballast tank, where the smaller particles are removed. The $Cl O_{2}$

is supplied from the $Cl O_{2}$

generator unit, where a small amount of water is directed through the generator by a booster pump [2]. Moreover, the water follows a flow through a venture, where vacuum is formed at the mixing chamber [2]. At this point, the chemical pumps provide the required amount of Purate and sulfuric acid into the chamber [2]. Thus, $Cl O_{2}$

is formed from the chemical reaction, that flows into the venture due to the former vacuum pressure created [2] Finally, $Cl O_{2}$

enters the supply water and then it is injected at the ballast water system.

2.1.3 System specifications

There are two main components for this BWTS, the filtration unit, which consists of parts, as showed in the Figure 2 and the treatment module, which consist of components, as shown in figure 3. This type of filters can handle flows from $550 - 1650 \frac{m^{3}}{H}$

and are automated cleaned. The overall system can handle variable flows from $400 - 12000 \frac{m^{3}}{h}$

with energy requirements from $7 - 62.6 kW$

as maximum and as typical $4.8 - 19.8 kW$

, as shown in figure 4 and 5.

2.1.4 System advantages and disadvantages

The advantage that offers the filter mechanism is the ability to self-clean, endure heavy loads of sediments and low energy requirements, due to low pressure operation. As far as concerns the treatment module, it can operate with low power consumption, automated and it does not require any changes on the current ballasting operation. Another benefit is that the treatment module can be placed in any convectional space on ship (relative small footprint). Possible disadvantages are that it requires safe storage, and handling on board, since the ClO₂can be explosive, if it is encountered with sparks, sun light and heat. Also, the filtration system needs to be changed in 5 and 10 years interval [6], so it should be matched with a drydocking period to avoid potential downtime of vessel.

2.2 Alfa Laval PureBallast

2.2.1 Working Principle

This type of arrangement utilized Ultra-violet (UV) reactor to achieve biological disinfection and the filtration process to remove the bigger organisms in the ballasting process. Also, it complies with convention of both USCG and IMO.

2.2.2 Process description

During ballasting condition, the incoming sea water goes through a filtration process, where the bigger organisms are getting removed; therefore, improving the quality of the incoming sea water. Afterwards, it goes into an enchanted UV reactor, where the biological disinfection occurs, before entering the ballast tanks [4]. Moreover, the cleaning in-place (CIP) cycle takes place, which is an automated process to clean up the reactor, by recirculating a non-toxic and biodegradable substance solution, and then to fill it up with fresh water, along with the filter. As far as concerns, the deballasting procedures the water goes into the UV reactor stage from the ballast tanks to remove potential organisms, that regrew and afterwards it is discharged into the receiving water at the deballasting site [4].

2.2.3 System specification

This type of arrangement can vary slightly, based on capacity application. The main units in all capacity application is the filter and UV reactor stage. The Pureballast Compact with capacity of $32 - 300 \frac{m^{3}}{h}$

, which consists of the following two supporting components the CIP and electrical cabinet, as shown in figure 7. The electrical cabinet provides the power for the reactor and can be placed 30m away from it, For Pureballast Complex with accommodated flow of $32 - 1000 \frac{m^{3}}{H}$

, the supporting components are CIP, electrical cabinet and LDC1/LDC2 (LDC1 provides power for flows $500 - 600 \frac{m^{3}}{H}$

and when combined with LDC2 for flows of $750 up to 1000 \frac{m^{3}}{H}$

) for flows above $300 \frac{m^{3}}{h}$

(figure 8). Finally, for larger flows $(250 - 3000 \frac{m^{3}}{H})$

the Pureballast 3 Std is utilized with supportive equipment of Lamp drive cabinet, CIP and control cabinet and two reactors, where each one can handle flows up to $1500 \frac{m^{3}}{H}$

, as shown in figure 9. The figures 10,11 and 12 represents the energy consumption of the above-mentioned arrangement at various flows of demand.

2.2.4 System advantages and disadvantages

This type of arrangement can operate at fresh, marine or brackish water [4]. Also, the power demand is significantly less, when the vessel operates within IMO regulations, about 42% in full flow rate [4]. Another advantage of this arrangement is that the system is fully automated. As far as concerns, the installation process it can be flexible, since the components are delivered as loose ones in case of Pureballast 3 Compact Flex and the lamp drive cabinet could be placed up to $150$

meters away for Pureballast 3 Ex (reference). Furthermore, the CIP unit does not require a remote-control dosage, since it is a closed loop system with reusable and non-toxic substance. On the other hand, the substance needs to be replaced every $3 - 12$

months and Lamp replacement every $3000$

hours of operation [4]. Also, the filter needs to be inspected every year. Finally, possible drawbacks could be the high cost of investment and the high-power consumption requirements in low-clarity water [4].

3.Suitability on ships

When considering the choice of BWTS on ships, there are several steps to be considered. First of all, the ballast water treatment system should meet the ballast capacity of the vessel. Moreover, the BWTS should have flexible installations procedures. Another important aspect, is the time required for the system to treat the water, so it might not be applicable depending on the streamline of the vessel. Compliance with both IMO and USCG could be crucial, because it can provide a wider range of offers, when deciding to sell the vessel. Also, the power consumption, maintenance and capital costs are important, as well. Whilst, considering the above in case of Alfa Laval BWTS, the reactor unit has a lifetime of over 20 years [5], which might not be ideal for a newbuilding ship with an expected lifetime of 25 years, since the maintenance costs will be considerably increased [5]. However, it has flexible capacity flow rate, which means it can be applied to all ship-types. Although, in large VLCC and ULCC with capacity of over $6000 \frac{m^{3}}{H}$

, this system is not that competitive, in terms of cost and power consumption. The Ecochlor BWTS can be applied to all ships, except in cases of small passenger ships with flow rates below $250 \frac{m^{3}}{H}$

. In terms of safety, Pureballast does not imply any immediate danger to the environment, crew and ship structure. However, in the Ecochlor BWTS, the substance is toxic and is refilled by the Ecochlor to avoid any potential accidents, since the system is approved by IMO and USCG it cannot provide any direct threat to the environment. As far as concerns ship structure the substance is a non-corrosive one. Also, the high production of this toxic gas could be a concern, if it leaks. However, there have not been any accidents and is mainly utilized on large bulk carriers (i.e. Panamax, Capesize) and tankers (Suezmax, VLCC). The maintenance cost of BWTS of Alfa Laval are shown in figure 14. Finally, based on Ecochlor president and founder, the maintenance costs for the chemical refill are typically $0.08$

USD$ per 1 m^3 of water treated [6]. Also, the filtration system needs to be replaced in intervals of 5 and 10 years with costs of $3600$

USD$ up to $12000$

USD$, depending on size and about $2000$

USD$ for miscellaneous maintenance activities [6]. The annual maintenance cost of Pureballast complex flex are shown in figure 14.

Reference

1. Imoorg. 2018. Imoorg. [Online]. [25 October 2018]. Available from: http://www.imo.org/en/MediaCentre/HotTopics/BWM/Documents/BWM infographic_FINAL.pdf

2. Ecochlorcom. 2015. Ecochlor. [Online]. [31 October 2018]. Available from: http://ecochlor.com/system/

3. Imoorg. 2018. Imoorg. [Online]. [31 October 2018]. Available from: http://www.imo.org:80/en/OurWork/Environment/BallastWaterManagement/Pages/Default.aspx

4. Alfalavalcouk. 2018. Alfalavalcouk. [Online]. [31 October 2018]. Available from: https://www.alfalaval.co.uk/microsites/pureballast/technical/

5. Anavees. 2018. Anavees. [Online]. [31 October 2018]. Available from: http://www.anave.es/images/documentos_socios/informe_sma/alfa_laval_pureballast.pdf

6. Ballastwatermanagementcouk. 2018. Ballastwatermanagementcouk. [Online]. [31 October 2018]. Available from: https://www.ballastwatermanagement.co.uk/news/view,counting-the-cost-of-ballast-treatment_42146.htm

Appendix

Figure 1. IMO info graph, relating the implementation of D1-D2 conventions. [1]

Figure 2. General arrangement of Ecochlor Filter system. [2]

Figure 3. Treatment module of Ecochlor BWTS. [2]

Figure 4. Technical data of smallest plant of Ecochlor BWTS [2]

Figure 5. Technical data of largest plant of Ecochlor BWTS [2]

Figure 6. Main components of Alfa Laval PureBallast 3.1. [4]

Figure 7. Alfa Laval PureBallast Compact $Capacity = 32 up to 300 \frac{m^{3}}{H})$

. [4]

Figure 8. Alfa Laval PureBallast Compact Flex $(Capacity = 32 up to 1000 \frac{m^{3}}{H})$

. [4]

Figure 9. Alfa Laval PureBallast Std Capacity (32-3000 m³/H). [4]

Figure 10. Technical data of Pureballast Compact Flex. [4]

Figure 11. Technical data of Pureballast Compact. [4]

Figure 12. Technical data of Pureballast Std. [4]

Figure 13. Table from ABS, regarding Ballast water.

Figure 14. Maintenance costs of Alfa Laval Compact Flex (up to $\frac{1000 m^{3}}{H}$

). [5]

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