To prevent Introduction of harmful aquatic species into new environments by shipping which have been thought to be a major threat to marine ecology and have been devastating in many areas of the , IMO adopted the Ballast Water Management Convention in 2004 at a diplomatic conference in London and eventually the convention entered into force on 17th September 2017.

More than 65 states representing more than 70% of the total world tonnage signed the BWM Convention

The BWMS Convention is composed of 22 Articles, and one Annex with 5 sections (A to E) which includes technical standards and requirements in the Regulations for the control and management of ships’ ballast water and sediments. 

Annex of the Convention

Annex – Section B “Management and Control Requirements for Ships”:

(Regulation B-1): Ships must implement and have on board a Ballast Water Management Plan approved by the Administration 

(Regulation B-2): maintain a Ballast Water Log Book to record ballast water movements (uptake, treatment, exchange, circulation, discharge)

Regulation B-3: the ships should adopt measures for ballast water management.

The specific requirements for ballast water exchange are contained in Regulation B-4 “Ballast Water Exchange”.

Annex – Section D “Standards for Ballast Water Management

Regulation D-1 “Ballast Water Exchange Standard” requires an efficiency of 95 per cent volumetric exchange of Ballast Water with marine water (at least 200 nautical miles from the nearest land and in water at least 200 metres in depth).

Regulation D-2 “Ballast Water Performance Standard” concerns water quality for discharge, related to specified maximum concentrations of micro-organisms.

IMO D-2 Standard for Discharge Ballast Water

Microorganism category Regulation

Regulation D-3: Ballast Water Management Systems must be approved by the Administration.

Annex – Section E “Survey and Certification Requirements for Ballast Water Management”

Implementation schedule for compliance with the D-2 standard

The amended regulation B-3, as approved by MEPC 71, require new vessels (vessels constructed/keel-laid on or after 8 September 2017) to comply with the D-2 standard and have a ballast water treatment system installed upon delivery. For existing vessels (vessels constructed prior to entry into force of the Convention), the MEPC stands by its decision to use the renewal of a vessel’s International Oil Pollution Prevention (IOPP) certificate as the mechanism to define the phase-in schedule but applying “on or after 8 September 2019” as the start of the phase-in period. As a result, the date by which all ships must have installed a ballast water treatment system has been extended from 2022 to 2024. 

The principles of the new implementation schedule for compliance with the D-2 standard is illustrated in the figure below and the details are provided 

EIF= Entered Into force

image source: Gard AS

To comply with annex D-2 of BWMS ship must have Ballast water treatment plant to attain the described standard of the ballast water.

The available ballast water technologies have been categorized as Mechanical, Physical and Chemical systems. Most of the on board treatment system is a combination of mechanical i.e filtration and followed by a physical/ chemical treatment 

At present UV system is the most popular ballast water treatment technique. The system uses ultraviolet rays to react with the DNA to make the organisms harmless as well as prevent reproduction.

ALFA LAVAL PURE BALLAST SYSTEM: AOT reactor working principle

UV lights housed inside the advanced oxidation treatment reactor,  inactivates the cell DNA to prevent regrowth of organisms. 

The UV light generates radical which are extremely reactive and react instantaneously with micro-organisms and other organic contaminants destructing their membranes. 

The number of extremely short-lived radicals are sufficient enough to treat the water as it passes through the reactor.

Image credit: alfa laval pure ballast system

Destruction of cell membranes

  1. Radical
  2. Cell membrane

Main components of the system:

 LDC (lamp drive cabinet):

The UV reactor is connected to a lamp drive cabinet containing lamp power supplies (LPS). The LPS also monitors the function of each UV lamp and takes action if a fault occurs. As LDC houses the LPS to switch on the UV lamps, it generates heat in the LDC. Before stating the plant, the LDC must be supplied with cooling water for the cooling.



The filter is a fully automatic self-rinsing component, equipped with an auto backwash mechanism.

The ballast water is led through the filter, and filtered particles are trapped in the filter which is removed by periodical backwash.

Back flushing for different dirt loads

The filter may become dirty with mud water in coastal areas or dirt may accumulate over time of its operation. Back flushing enables the dirt to be washed away without dismantling the filter but while the filter is in operation.

Actuating principle:  The outlet valve from the UV reactor is throttled to 70-80%. As a result, pressure is increased inside the filter body. An electric motor mounted on the top of the filter starts to rotate and from the inner chamber of the filter an outlet is opened to the overboard. This carries all the deposits from the filter. Back flush operates if the pressure differential is more than 0.5 Bar or at 30 minutes intervals.

UV reactor chamber:

–         The first condition to activate the UV reactors is cooling water flow. The UV lights generate a lot of heat, if there is no water or little water than required the UV lights may damage. There are sensors to ensure the flow of water. Water sensors will send signals to the LDC and LDC will gradually (normally 90 Seconds) light up the UV lights.


 Operation conditions:

Before operating the plant, the operator must ensure;

  • Control air supply is sufficient to operate the ballast water valves
  • Cooling water supply to the LDC 
  • Cooling water supply to the UV reactor chamber. UV lights generates tremendous heat. If it starves of cooling water the UV lights may damage. 
  • there is no alarm activated in the monitor.

The bypass valve makes it possible to bypass the entire system, for example to secure ballast operation if the system is not functioning.



Ballasting and de-ballasting begins with a start-up phase.

–         There must be available power for the system

–         During start-up, the UV lamps are warmed up for 90 seconds.

–          Cooling water must be supplied to the UV reactor to secure that the UV lamps are not overheated generated by the lamps.

–         Temperature transmitter and level switch are fitted  to ensure that there is water in the UV reactor and that the UV lamps are sufficiently cooled. If not, an alarm is issued and the system is shut down.

Ballast process:

This mode of operation uses both the filter and UV reactor chamber while ballasting.

The flow direction is

Ballast pump—– filter ———— flow meter——-UV chamber———over board.

Image credit: Alfa Laval Pure Ballast System

-After the start-up sequence once the lamps are ready, the operator is requested to start the ballast pump.

– The ballast water is pumped to the filter which removes larger particles and organisms. This also reduces the amount of sediment build-up in the ballast water tanks. The organisms and sediments caught in the filter are flushed overboard via regular filter backflush operations.

 – The water is finally led to the UV reactor, which produces radicals and UV light that breaks down and neutralized the organisms.



Deballast process”

The de-ballasting process only uses the UV chamber and filter remains closed.

Ballast pump—flow meter——-UV chamber———over board.


Image Credit: Alfa Laval Pure Ballast System

After the start-up sequence once the lamps are ready, the operator is requested to start the ballast pump.

The water passes through the UV reactor for second time to ensure that the treatment is fully effective. The minor part of the organisms, which were only injured during ballast, will be rendered totally harmless during the de-ballast.


CIP (Cleaning in Place):


It enables the filters and UV reactor chamber to be chemically cleaned without dismantling or opening them. CIP has to be done after every operation within 30 hrs.


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