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General guidance for prevention of marine pollution by sewage

Sewage is human body waste and the waste from toilets and other receptacles intended to receive or retain body waste which is discharged from the vessel .Sewage is naturally rich in both phosphorous and nitrogen, which encourage the excessive growth of plants and algae creating toxic algae ‘blooms’.

When these plants and algae die, they are decomposed by bacteria that also remove oxygen from the water, killing other marine life.

Sewage is also a source of pathogens such as viral hepatitis, cholera, typhoid fever, and a range of stomach and intestinal diseases. MARPOL 73 / 78 Annex IV

Regulations for the Prevention of Pollution by Sewage of Ships entered into force on 1 August 2005 and apply to new and existing ships of:

•400+ gross tonnage
•less than 400 gross tonnage certified to carry more than 15 persons.
*'New ship' is one for which the building contract or keel was laid on or after 27 September, 2003 or delivered on or after September 23, 2006.
* Existing ships had to comply by 27 September 2008

Revised Sewage Standards

The Marine Environment Protection Committee (MEPC) at its 55th session in October 2006, adopted revised guidelines on sewage treatment plants (see resolution MEPC.159(55)). The revised guidelines apply to sewage treatment plants installed on or after 1 January 2010.

The MEPC also adopted a standard for the maximum rate of discharge of untreated sewage from holding tanks when at a distance equal or greater than 12 nautical miles from the nearest land (see resolution MEPC.157(55)).

Marpol annex IV was revised and updated by IMOs Marine Environment Protection Committee (MEPC) in 2000, and came into force on 27 September 2003. It applies to vessels engaged in international voyages, and sets out in detail how sewage should be treated or held aboard ship, and the circumstances in which discharge into the sea may be allowed.



This Annex applies to all new ships (built after the date of entry into force of the Annex) of 400 gt and over, and to new ships of less than 400 gt which are certified to carry more than 15 persons.

Five years after its entry into force i.e. from 27 September 2008, the Annex will also apply to existing ships of 400 gt and over, and to existing ships of less than 400 gt which are certified to carry more than 15 persons. The Master shall prevent marine pollution by complying with “MARPOL Annex IV” and any local or domestic law and regulations.

“Sewage” means:

1. Drainage and other waste from any form of toilet

2. Drainage from medical premises (hospital etc.) via wash basins and scuppers located in such premises

3. Other wastewaters when mixed with the drainage defined above


Prohibition on Sewage Discharge

The discharge of sewage into the sea is prohibited, except when:

• The ship has in operation an approved Sewage Treatment Plant which has been certified by the flag state, and the effluent does not produce visible floating solids in, nor cause discoloration of the surrounding water, OR

• The ship is discharging the sewage at a distance of more than 12 miles from the nearest land, and proceeding at not less than 4 knots (in case Plant stopped for maintenance)

Where the vessel is operating in waters under the jurisdiction of a State where the local requirements are more stringent than above, these shall be complied.

The Chief Engineer or Officer is to confirm that the sewage overboard valves is positively locked in the closed position to ensure no accidental direct discharge.


Sewage Treatment Plant

The Master shall keep on board the certificate of type-approval of the Sewage Treatment Plant including the USCG Certification (provided by the manufacturer).


Operation and Maintenance of Sewage Treatment Plant

The Master shall designate the officer in charge to have him carry out the following matters:

1. Keep operating the Sewage Treatment Plant all the time, in principle.

2. The inspection and maintenance shall be done in accordance with the Makers Instruction Book.

For the type which requires addition of chemicals, these should be stocked, and added as required by manufacturer’s instruction.

Rules and Regulations for Reference :

• MARPOL Annex IV (IMO)
• U.S. Regulation, 33CFR, Part 159 (Marine Sanitation Device)


California No Discharge Zone Prohibiting Vessel Sewage in all California Marine Waters

Effective March 28, 2012, the following vessels will be prohibited from discharging all sewage, whether treated or not, while in California marine waters:

• Large Passenger Vessels of 300 gross tons or greater that have berths or overnight accommodations for passengers.

• Large Oceangoing Vessels of 300 gross tons or greater, including private, commercial, government, or military vessels equipped with a holding tank with remaining capacity or containing sewage generated prior to entry in to California marine waters.


Related articles

  1. Marpol annex I - Preventing pollution by oil -Notes on Oily Water Separators


  2. Marpol Annex II -Noxious Liquid Substances in Bulk


  3. Marpol annex III -Pollution by other harmful substances & harmful packaged goods


  4. Marpol annex IV - Prohibition on Sewage Discharge


  5. Marpol annex V - Pollution by garbage


  6. Marpol annex VI - Pollution by air


  7. Prohibition on use of harmful (TBT) anti-fouling paints


  8. Pollution by ballast water


  9. Prevention of pollution while carrying out overboard maintenance


  10. Environment friendly purchasing


  11. Environmental awareness


  12. Burning of heavy fuel oil & diesel oil - Environmental impacts




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