With regard to the Ballast Water Management Convention:

(Refer to detailed answers above for D-1, D-2, and treatment methods.)

• Physical separation: filtration (screens/disc filters) to remove larger organisms and sediment.
• Mechanical/inactivation: ultraviolet (UV) irradiation, ultrasound/cavitation.
• Chemical disinfection: electro-chlorination (generating chlorine/oxidising biocide from seawater), ozone, and addition of chemicals (e.g. chlorine, sodium hypochlorite, peracetic acid, or oxidants). HydroF-
• Treatment generally combines filtration + UV or filtration + electro-chlorination to reduce organics and achieve the D-2 standard.
• The method must be effective across the ship's ballast water salinity/temperature and suited to the flow rate (the system must be type-approved).

• Non-active substances: systems (e.g. simple filtration, UV) that do not use active (biocidal) substances are "based on physical/non-active methods"; the system is assessed by the Administration for type approval considering the IMO's Basic Approach/Type Approval Guideline and the BW code; approval is granted after meeting the environmental acceptance criteria (e.g. no discharge of chemicals above safe levels).
• Active substances: systems that use biocides/oxidants (electro-chlorination, ozonation, chemical dosing) must satisfy the IMO's "two-tier" approach: (1) a basic approach for approval of the active substance/method by GESAMP (the joint group of experts) - the "active substance" is reviewed for environmental and human health acceptability, generating an evaluation/protocol; (2) methods to be approved at the system level (type approval of the BWMS) by the Administration/flag State following the accepted test protocol (the IMO G8 redesignated to BWMS Code). In practice: the active substance approval is submitted to the relevant technical body (GESAMP and the MEPC) which assesses human and environmental safety, and the system is then type-tested. The type approval only applies to that specific system; an "ad-hoc/decision" and the correct treatment records.
• The relevant approval route is that the system must meet the "BWMS Code" (International Code for Approval of Ballast Water Management Systems) which requires salinity, temperature, flow tests, and testing with representative ballast, plus reliability, and the environmental acceptance criteria for active substances (the residual biocide concentration). This balances the effectiveness (achieving D-2) with safety to the receiving environment and crew.