The D-1 and D-2 standards
The Convention sets two standards. D-1 is ballast water exchange, conducted at distance from shore to reduce the organisms carried. D-2 is the performance standard met by an approved ballast water treatment system, which limits the number of viable organisms that may be discharged. Ships have transitioned to the D-2 standard, generally tied to their renewal survey schedule.
Treatment systems and records
Most vessels meet D-2 with an installed ballast water treatment system, type-approved and operated within its limits. Accurate ballast operations records are essential, incomplete or inconsistent records are a common inspection finding even when the equipment is sound.
Operational discipline
Compliance is as much about operation as installation: knowing where and when exchange or treatment is permitted, maintaining the system, and recording every operation correctly. It is an area where a clear procedure and good record-keeping prevent most problems.