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Types of BW treatment/management systems
If your vessel has not yet been fitted with a BWTS that complies with the new requirement, your ballast water should always be discharged and taken on board mid-ocean (not near shore).
Sooner, rather than later, your vessel will need to be upgraded to comply. The new BWM Convention standards are being phased in for ships currently in operation, but new vessels need to be equipped with modern ballast water treatment equipment to meet the new standards.
Choose the correct type of BWTS
Ballast water is usually filtered in two stages. After passing through the initial large filter, which is similar for all ballast water treatment systems, ocean water that is taken on board for ballast needs to proceed through a second filtration system to get rid of smaller, even microscopically small organisms and substances.
Eight different types of filtration processes are in use around the world.
- Physical Separation or Filtration Systems
These systems remove microscopic and other sea life as well as solids either from the sediment or from the surface of the water. The backwash containing the unwanted material is then either discharged into the ocean from where the water was taken, or it is held and treated on board for use as ballast in the tanks, from where it can be discharged (without any marine life left in it) in a different location when the need arises.
- UV Systems
Ultraviolet purification systems combine physical filtration and UV technology. In such a system, the ballast water flows through a chamber that is surrounded by UV lights. The UV radiation “sterilizes” the marine organisms. They become harmless and unable to reproduce.
- Chemical Treatment
Special oxidizing and non-oxidizing biocides of the types that that have been proven effective in combating marine organisms are added to the ballast water. These biocides are chosen for their effectiveness and also for their ability to biodegrade or to be removed easily to prevent the ballast water from becoming contaminated by toxins.
Oxidizing biocides include chlorine, bromine and iodine. These disinfectants destroy the cell membrane or nucleic acids of the microorganisms.
Non-oxidizing biocides counteract the reproduction and the neural or metabolic functions of the organisms.
Nitrogen or other inert gas is injected into the space above the water level in the ballast tanks. This causes the oxygen in the water to be removed. Without oxygen, the marine organisms become asphyxiated and die. The process takes two to four days. For the deoxygenation to succeed, the ballast tanks need to be perfectly airtight.
- Heat Treatment
The ballast water is heated to a temperature that’s high enough to kill the organisms. A dedicated heating system can be installed to heat the water in the tank. Alternatively, the ballast water could be piped to cool the vessel’s engine. The cooling water then becomes heated by the engine’s heat, and it kills the suspended organisms. This is a slow process, which could also cause tanks to corrode.
- Electric Pulse and Pulse Plasma Treatments
In this system, which is still in development, short blasts of energy are produced in the ballast water to kill the organisms. The treatment is done in one of two forms:
In the pulse electric field technology, two metal electrodes generate the energy pulse at very high power density and pressure.
In electric plasma technology, a plasma arc is generated to kill the organisms.
- Ultrasonic or Cavitation Treatment
In this treatment, ultrasonic energy produces high energy ultrasound in the ballast water, the impact kills the cells of the suspended organisms. Ultrasonic or cavitation techniques are generally used together with other systems.
- Magnetic Field Treatment
This is a type of flocculation treatment. Magnetic powder is mixed with coagulants and added to the ballast water in the tank. Magnetic flocs or flakes are formed. These can contain large quantities of marine organisms. Magnetic discs are used to lift the flocks from the water and the contents are disposed of safely.
Which system is the most suitable depends on various factors, including the following:
- flow ballast water (m³/hr)
- total amount of ballast water to be cleaned
- new build or retrofit
- company’s policy about waste disposal (chemical)
- sailing USA water or not (US Coast Guard regulations).
MR Ballast services any type of ballast water treatment system, helping to ensure ships’ compliance and clean oceans worldwide.