Zero discharge mode

Zero discharge mode is operation in which a ship discharges nothing to the sea, holding all oily bilge water, sewage, gray water, garbage, scrubber washwater, and ballast for delivery to reception facilities or for discharge only outside restricted waters. It is required in MARPOL special areas, designated emission and discharge zones, many ports and inland waters, and increasingly demanded by charterers and terminals. The crew relies on holding-tank capacity, the Oil Record Book, the Garbage Record Book, and the Ballast Water Record Book to prove no discharge took place. The mode is operational rather than a single regulation; the underlying limits come from the relevant MARPOL annex and local rules.