Ballast water treatment system (BWTS)

A ballast water treatment system (BWTS) treats ballast water on uptake, discharge, or both so the effluent meets the IMO BWM Convention D-2 standard: fewer than 10 viable organisms per cubic meter that are 50 micrometers or larger, and fewer than 10 viable organisms per milliliter in the 10 to 50 micrometer band, plus bacterial indicator limits. Two technology families dominate: filtration plus UV irradiation, and filtration plus electrolytic or injected chlorination. The goal is to stop transfer of invasive species between ports. USCG type approval is separate from IMO approval and uses the most-probable-number viability method, so a system can hold one and not the other.