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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 ships, engaged in international voyages, of 400 gross tonnage and above or which are certified to carry more than 15 persons. 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 when the ship is en route and proceeding at not less than 4 knots, and the rate of discharge of untreated sewage shall be approved by the Administration (see resolution MEPC.157(55))
Currently, the Baltic Sea area is the only Special Area under Annex IV. In accordance with resolution MEPC.275(69), the discharge requirements for Special Areas in regulation 11.3 of MARPOL Annex IV for the Baltic Sea Special Area shall take effect:
on 1 June 2019, for new passenger ships[1];
on 1 June 2021, for existing passenger ships[1] other than those specified in .3; and
on 1 June 2023, for existing passenger ships en route directly to or from a port located outside the special area and to or from a port located east of longitude 28˚10′ E within the special area that do not make any other port calls within the special area.Q: What are the standards for Sewage Treatment Plants?
A: Sewage treatment plant installed prior to 01 January 2010 shall comply with resolution MEPC.2(VI); or
ii. sewage treatment plant installed on or after 01 January 2010 but prior to 01 January 2016 shall comply with resolution MEPC.159(55); or
iii. sewage treatment plant installed on or after 01 January 2016 shall comply with resolution MEPC.227(64).Q: What’s the requirements of MEPC.159(55)?
A: The sewage treatment plant was tested and produced an effluent which, on analysis, produces:
(i) a geometric mean of no more than 100 thermotolerant coliforms/100 ml;
(ii) a geometric mean of total suspended solids of 35 mg/l if tested ashore or the maximum total suspended solids not exceeding 35 plus x mg/l for the ambient water used for flushing purposes if tested on board;
(iii) a geometric mean of 5-day Biochemical Oxygen Demand (BOD5) of no more than 25 mg/l;
(iv) a geometric mean of Chemical Oxygen Demand of no more than 125 mg/l;
(v) pH of the effluent is between 6 and 8.5.
The Administration is satisfied that the sewage treatment plant can operate at angles of inclination of 22.5° in any plane from the normal operating position.Q: What’s the requirements of MEPC.227(64)?
A: The sewage treatment plant was tested and produced an effluent which, on analysis, produces:
.1 a geometric mean of no more than 100 thermotolerant coliforms/100 ml;
.2 a geometric mean of total suspended solids of 35 Qi/Qe mg/l if tested ashore or the maximum total suspended solids not exceeding (35 plus x) Qi/Qe mg/l for the ambient water used for flushing purposes if tested on board;
.3 a geometric mean of 5-day biochemical oxygen demand without nitrification (BOD5 without nitrification) of no more than 25 Qi/Qe mg/l;
.4 a geometric mean of chemical oxygen demand (COD) of no more than 125 Qi/Qe mg/l;
.5 pH between 6 and 8.5;
.6 a geometric mean of total nitrogen of no more than 20 Qi/Qe mg/l or at least 70 per cent reduction; and
.7 a geometric mean of total phosphorus of no more than 1.0 Qi/Qe mg/l or at least 80 per cent reduction**.The Administration confirms that the sewage treatment plant can operate at angles of inclination of 22.5° in any plane from the normal operating position.
Source: https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.227(64).pdf
Q: Can this approved Sewage Treatment Plant pump treated sewage overboard < 3 Nm to the nearest shore? A: If the nearest shore's Administration allows, then the answer is yes. Always refer to the local regulations, such as USA's No Discharge Zones (NDZ).
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