What are the MARPOL discharge criteria under Annex II and Annex IV?
Short answer
| Annex II noxious liquid substances | Annex IV sewage | |
|---|---|---|
| Speed | en route at least 7 knots (4 if not self-propelled) | en route at not less than 4 knots, at a moderate rate |
| Distance from land | more than 12 nautical miles | treated more than 3, untreated more than 12 nautical miles |
| Depth and outlet | not less than 25 metres, below the waterline | — |
| Treatment | per the P&A Manual; Category X prewashed to a reception facility | comminuted and disinfected, or approved treatment-plant effluent |
- Annex II (regulation 13): only en route at least 7 knots (4 if not self-propelled), below the waterline within the designed rate, more than 12 nautical miles from land, depth not less than 25 metres, per the P&A Manual.
- Category X (regulation 6: X, Y, Z): prewash to a reception facility down to 0.1% by weight, residues never to sea; Y and Z stripped, then discharged under the conditions.
- Annex IV systems (regulation 9): an approved sewage treatment plant, a comminuting and disinfecting system with a holding tank, or a holding tank.
- Annex IV discharge (regulation 11): treated (comminuted and disinfected) more than 3 nautical miles from land, untreated more than 12, at a moderate rate en route at not less than 4 knots; or approved treatment-plant effluent.
- Common threads: en route at a minimum speed, a minimum distance from land, an approved system; exceptions for safety or damage (regulation 3).
- As Chief Engineer: the sewage plant is mine; discharge only within the criteria, and recorded.
Full answer
The full answer explains each point step by step, with the regulations and figures behind it and the discussion from other candidates. It is in the MEO Class I section of the Marine One forum, open to members enrolled for the MEO Class I exam.