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Ballast Water Treatment Systems at a glance

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Martin Olofsson Martin Olofsson
Senior Principal Engineer

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Treat Her Right
Ballast water management is among the top environmental issues addressed by new regulations.
With the ratification of the Ballast Water Management Convention, shipowners are pressed to decide which treatment systems to choose. For manufacturers keen to be selected, attaining type approval by the U.S. Coast Guard can be a deciding factor. DNV GL provides comprehensive support.
Treat Her Right
Optimarin received USCG type approval for its filter/UV system in 2016.

After many years of discussions, the date is set. The IMO’s Ballast Water Management Convention will enter into force on 8 September 2017. For operators with vessels that discharge ballast water in international waters, this means that they must have a treatment system installed on their vessels within five years. The specific deadline depends on the next renewal survey of a vessel’s International Oil Pollution Prevention (IOPP) certificate.

For many operators trying to decide which type of system to install, one of the most important questions is: Does the system meet the U.S. Coast Guard (USCG) requirements? In late 2016, the manufacturers Alfa Laval, Optimarin and OceanSaver became the first to be awarded U.S. Coast Guard type approval certificates for their ballast water treatment systems. “We are proud to have worked with all three of these successful applicants from the very beginning,” says Martin Olofsson, Senior Principal Engineer, Environmental Protection DNV GL – Maritime Approval of Ship Systems and Components.

More systems close to approval

In the first quarter of 2017, DNV GL submitted two further applications to the U.S. Coast Guard, for manufacturers Sunrui and Ecochlor. “Currently, we have also completed land-based testing cycles for four further manufacturers. Successfully passing land-based testing is a good indication that the systems could also meet the U.S. Coast Guard’s requirements, once they have undergone shipboard testing,” says Olofsson. “Land-based testing really challenges the efficacy of these systems. In 15 test cycles, they expose the systems to 1,000 times more large organisms and ten times more medium-sized organisms than shipboard testing.” If all goes to plan, another four systems could be approved in the first half of 2018.

The USCG officially appointed DNV GL as an Independent Laboratory (IL) to perform type approval testing of ballast water treatment systems (BWTS) in 2013. “DNV GL and its associated sub-laboratories DHI Denmark, NIVA (Norway), Golden Bear Facility (USA) and DHI Singapore have been deep into the details of USCG testing for three years and have gained substantial experience in what is practical and possible to achieve in compliance with the regulation,” says Olofsson. There are now five “Independent Laboratory” accreditations for BWTS. Out of 45 BWTS manufacturers who have signed a letter of intent for having their systems approved by the USCG, DNV GL is currently handling 25, making it the largest independent provider of laboratory services by far.

The choice of the best-suited treatment system for a particular vessel depends on a number of factors: What ship type is it? Does the vessel operate in fresh or brackish water? Does it primarily sail in cold or temperate waters? Will the system have to work in high-turbidity conditions, meaning water that contains a lot of clay, algae or silt? All these questions are very important for making the right choice. The five treatment systems which already hold or are soon expected to hold a USCG type approval certificate include UV systems, electrolytic systems and chemical injection systems. Read on to see how these types of systems work, which operational profiles they can handle and their advantages and drawbacks.

UV SYSTEMS

How it works
Suitable for
Advantages/Challenges
How it works
With a market share of 50 per cent, UV systems are the most popular option at present. They use a two-step process of filtration and ultraviolet (UV) irradiation to sterilize organisms and stop their reproduction.
Suitable for
UV systems are suitable for any vessel in theory, but primarily for those which do not take in too much ballast water and have flow rates of up to around 1,000 cubic metres per hour. This includes ro-ro vessels, container ships, offshore supply vessels and ferries.
Advantages/Challenges
UV systems are easy to install and retrofit, and have few safety concerns from a class point of view. They also operate independently, no matter what the water salinity and temperature are. However, they are dependent on the water transmittance (UV-T) and work less well in turbid water. The U.S. Coast Guard’s interpretation that any organisms released into US waters should be dead before leaving the vessel, rather than just made infertile, means that a type-approved filter+UV system becomes more sensitive to water turbidity and may require longer holding times to ensure mortality.

ELECTROLYTIC SYSTEMS

How it works
Suitable for
Advantages/Challenges
How it works
Electrolytic treatment systems have a market share of around 35 per cent and therefore come second in the treatment systems’ ranking. Many of these systems also use a filter as a pretreatment. By passing an electric current through a small side-stream of seawater, they use the salt and the water molecules in a chemical reaction to generate sodium hypochlorite, a disinfectant, which is then reinjected into the ballast water to kill all organisms.
Suitable for
Electrolytic treatment systems are more suited for larger vessels such as tankers and bulk carriers, which have large ballast water volumes and high flow rates in the range of up to 8,000 cubic metres per hour.
Advantages/Challenges
As well as being able to handle large capacities, electrolysis-based systems are very efficient and the treatment of the water is done on the intake only (possible neutralization on discharge). This means they provide on-board disinfection, and some systems even provide in-tank circulation treatment during the voyage, when treatment in the port is not feasible. One of the disadvantages is that the electrolytic reaction generates small amounts of hydrogen gas, a factor which needs to be accounted for in safety considerations. In addition, electrolytic systems are sensitive to low salinity and low temperatures, so salt or a heating system must be added where necessary. Finally, they are more complex to install, control and maintain compared to UV filter systems.

CHEMICAL INJECTION SYSTEMS

How it works
Suitable for
Advantages/Challenges
How it works
These systems are often used in combination with filtration. A chemical solution is injected into the ballast water to ensure disinfection. The disinfectant may be liquid or granular and will sometimes require neutralization prior to discharge overboard. Some of the active substances which are commonly used include sodium hypochlorite, peracetic acid and chlorine dioxide.
Suitable for
Chemical injection systems are deemed appropriate for most ballast flow capacities ranging up to 16,000 cubic metres per hour and are mostly used to treat ballast water on vessels with larger capacities and flow rates, such as tankers and bulkers. The technology also makes it suitable for infrequent usage and is also good for disinfecting tanks that have been used without treating the ballast water during ballasting and deballasting in local waters.
Advantages/Challenges
Chemical injection systems generally have low power requirements, because their only energy consumption comes from distributing the chemicals into the ballast water. With the dosing pump as their main component these systems require less space on board, making them easier to install than other technologies. However, the chemicals which are used, such as Peraclean or Purate, are trademarked, and supply might be limited to specific ports. In addition, the chemicals must be stored on board in closed containers and may be hazardous. The use of chemicals requires implementation of strict safety provisions and crew training. Having to stock up the supply of chemicals regularly also generates additional operational costs compared to UV or electrolysis systems, which have electricity as their main cost item.