Prevention of Pollution by Sewage from Ships


Regulations for the prevention of pollution by sewage are contained in Annex IV of MARPOL.

Sewage – the problem

The discharge of raw sewage into the sea can create a health hazard. Sewage can also lead to oxygen depletion and can be an obvious visual pollution in coastal areas - a major problem for countries with tourist industries.

The main sources of human-produced sewage are land-based - such as municipal sewers or treatment plants. However, the discharge of sewage into the sea from ships also contributes to marine pollution.

Annex IV of MARPOL

Annex IV contains a set of regulations regarding the discharge of sewage into the sea from ships, including regulations regarding the ships' equipment and systems for the control of sewage discharge, the provision of port reception facilities for sewage, and requirements for survey and certification.

It is generally considered that on the high seas, the oceans are capable of assimilating and dealing with raw sewage through natural bacterial action. Therefore, the regulations in Annex IV of MARPOL prohibit the discharge of sewage into the sea within a specified distance from the nearest land, unless otherwise provided.

Governments are required to ensure the provision of adequate reception facilities at ports and terminals for the reception of sewage, without causing delay to ships.

The Annex entered into force on 27 September 2003. A revised Annex IV was adopted on 1 April 2004 and entered into force on 1 August 2005.

The revised Annex applies to new ships engaged in international voyages of 400 gross tonnage and above or which are certified to carry more than 15 persons. Existing ships are required to comply with the provisions of the revised Annex IV five years after the date of entry into force of Annex IV, namely since 27 September 2008. The Annex requires ships to be equipped with either an approved sewage treatment plant or an approved sewage comminuting and disinfecting system or a sewage holding tank. 

The discharge of sewage into the sea is prohibited, except when the ship has in operation an approved sewage treatment plant or when the ship is discharging comminuted and disinfected sewage using an approved system at a distance of more than three nautical miles from the nearest land. Sewage which is not comminuted or disinfected may be discharged at a distance of more than 12 nautical miles from the nearest land, and the rate of discharge of untreated sewage shall be approved by the Administration (see resolution MEPC.157(55))

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

Special area

A special area established under Annex IV is the Baltic Sea area.

In July 2011, MEPC 62 adopted, by resolution MEPC.200(62), the most recent amendments to MARPOL Annex IV, which entered into force on 1 January 2013. The amendment introduces the Baltic Sea as a special area under Annex IV and adds new discharge requirements for passenger ships while in a special area. 

The discharge of sewage from passenger ships within the special area will generally be prohibited under the new regulations, except when the ship has in operation an approved sewage treatment plant which has been certified by the Administration (see resolution MEPC.227(64)). The sewage treatment plant installed on a passenger ship intending to discharge sewage effluent in special areas should additionally meet the nitrogen and phosphorus removal standard when tested for its Certificate of Type Approval by the Administration (resolution MEPC.227(64)​, section 4.2).

The date on which the requirements in respect of the special area will take effect depends on sufficient notifications to IMO from the Parties bordering the Baltic Sea, on the availability of reception facilities for sewage.​​