Discharge Criteria

Discharge criteria are the quantitative conditions each MARPOL annex sets before a residue stream may go overboard. Annex I Regulation 15 allows oily water only below 15 ppm with the oil filtering equipment running, the ship under way, and outside special areas. Annex II grades noxious liquid substances X, Y, and Z with prewash and concentration limits. Annex IV sets sewage discharge distances and rates. Annex V permits only specific garbage types at stated distances, with comminuted food waste allowed beyond 3 nautical miles. Inside special areas every threshold tightens, often to a full discharge prohibition.