Regulations on Discharge of Sewage

General Requirement:

• This regulation comes under MARPOL Annex IV, Chapter 3 - Equipment and Control of Discharge, Regulation 11.

• When the sewage is mixed with wastes or water covered by other Annexes of MARPOL, the requirements of those Annexes shall be complied with in addition to the requirements of this Annex.

Discharge of Sewage from ships other than Passenger ships in all areas and discharge of Sewage from Passenger ships Outside Special areas:

1. Subject to the provision of this Annex, the discharge of sewage into the sea is prohibited, except when:

1. The ship is discharging comminated and disinfected sewage using a system approved by the Administration in accordance with Regulation 9 of this Annex at a distance of more than 3 nautical miles from the nearest land, or sewage which is not comminated or disinfected at a distance of more than 12 nautical miles from the nearest land, provided that, in any case, the sewage that has been stored in holding tanks, or sewage originating from the spaces continuing the living animals, shall not be discharged instantaneously but at a moderate rate when the ship is en route and proceeding at not less than 4 knots; the rate of discharge shall be approved by the administration based upon standards developed by the Organization. 
2. The ship has in operation an approved sewage treatment plant that has been certified by the administration to meet the operational requirements of this Annex, and the effluent shall not produce visible floating solids nor cause discolouration of the surrounding water.

2. The provision of the above paragraph shall not apply to ships operating in the waters under the jurisdiction of a state and visiting ships from the other states while they are in these waters and are discharging sewage in accordance with such less stringent requirements as may be imposed by such state. 

Discharge of Sewage from Passenger ships within a special area:

3. Subject to the provisions of this Annex, the discharge of sewage from a passenger ship within a special area shall be prohibited:

1. For New Passenger ships, on a date determined by the Organization under the regulation of this Annex, but in no event prior to 1 June 2019
2. For existing Passenger ships, on a date determined by the Organization under the regulation of this Annex, but in no event prior to 1 June 2021

4. Discharge of the Sewage from a passenger ship within the Special area shall be prohibited except when the following conditions are satisfied:

1. The ship has an approved sewage treatment plant that has been certified by the Administration to meet the operational requirements referred in Regulation 9 of this Annex, and the effluent shall not produce visible floating solids nor cause discolouration of the surrounding water.

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Reference: IMO Publications & Documents - International Conventions - MARPOL - Annex IV