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 facilities at ports and terminals for the reception of sewage, and requirements for survey and certification. It also includes a model International Sewage Pollution Prevention Certificate to be issued by national shipping administrations to ships under their jurisdiction.
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 of the nearest land, unless they have in operation an approved sewage treatment plant.
Governments are required to ensure the provision of adequate reception facilities at ports and terminals for the reception of sewage.
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 has to be discharged at a distance of more than 12 nautical miles from the nearest land.
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)).
In July 2011, the Marine Environment Protection Committee, at its sixty-second session, adopted the most recent amendments to MARPOL Annex IV by resolution MEPC.200(62) which will enter 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 a special area will generally be prohibited under the new regulations, except when the ship has in operation a sewage treatment plant which shall be of a type approved by the national Administration (see section below).
Revised sewage standards
MEPC at its sixty-first session in autumn 2010 recognized that the Revised Guidelines on Implementation of Effluent Standards and Performance Tests for Sewage Treatment Plants (see resolution MEPC.159(55)), which were adopted in October 2006 and which apply to sewage treatment plants installed onboard on or after 1 January 2010, would need updating in view of the new Annex IV requirements mentioned above.
Accordingly, MEPC 61 instructed the Sub-Committee on Ship Design and Equipment to carry out this work. The
Sub-Committee, at its fifty-fifth session in March 2011, agreed to establish a Correspondence Group on the Revision of resolution MEPC.159(55), who made good progress in developing the revised guidelines. At its fifty-sixth session in February 2012 the Sub-Committee agreed, in principle, to a draft MEPC resolution on Guidelines on Implementation of Effluent Standards and Performance Tests for Sewage Treatment Plants, which was prepared by a working group established at that session. However, no consensus was found regarding the total nitrogen and phosphorous removal standards for passenger ships intending to discharge sewage effluent in special areas. The Sub-Committee will therefore submit the draft MEPC resolution to the sixty-forth session of the Marine Environment Protection Committee in October 2012, who will be invited to decide on the nitrogen and phosphorous removal standard and adopt the guidelines accordingly.