Open-loop scrubber discharge restrictions
Port and coastal States restrict or ban exhaust gas cleaning system discharge water in their own waters under their own jurisdiction, not under any IMO instrument.
Open-loop discharge restrictions are the single largest operational constraint on a scrubber ship, and they do not come from MARPOL. No provision of Annex VI authorises a port or coastal State to impose a stricter discharge standard on a ship exercising the Regulation 4 equivalence . Restrictions rest instead on the State’s own jurisdiction over its ports, internal waters and territorial sea, which is why the register changes without any IMO amendment and why it has to be checked voyage by voyage rather than learned once.
Resolution MEPC.1/Circ.899, the 2022 Guidelines for risk and impact assessments of the discharge water from exhaust gas cleaning systems, is the IMO’s answer to the resulting patchwork: it gives a State a common method for assessing local impact before it acts, and gives owners a common framework for arguing about the result.
Inside the Mediterranean SECA the restrictions are national or port-level, such as France’s 3-nautical-mile band.
The full article will carry the restriction register with each entry sourced to the issuing authority’s own circular or legal instrument, distinguish a ban on discharge from a ban on operation, separate berth-only from territorial-sea restrictions, and cover the hybrid scrubber and holding-tank workarounds.