What Is MARPOL Annex IV? A Guide to Sewage Pollution from Ships

A simple way to remember this is:

Treated/comminuted sewage → more than 3 NM
Untreated sewage → more than 12 NM + en route + minimum 4 knots

Approved Sewage Treatment Plants

Ships operating an approved STP may discharge treated effluent according to the applicable Annex IV requirements.

The effluent must not:

• Produce visible floating solids; or
• Cause discoloration of the surrounding water.

Standard Discharge Connection

Regulation 10 requires a standard sewage discharge connection so ships can transfer sewage to shore reception facilities.

This allows ships and ports to use a standardized connection during sewage discharge ashore.

Surveys and ISPP Certificate

Ships subject to Annex IV undergo:

• Initial surveys;
• Renewal surveys; and
• Additional surveys when required.

Compliant ships are issued an International Sewage Pollution Prevention Certificate (ISPP Certificate). The certificate is normally valid for a maximum of five years, subject to the required surveys and endorsements.

Special Areas

Annex IV provides stricter sewage controls in designated special areas.

The Baltic Sea area is designated as a special area under Annex IV.

Passenger ships operating within applicable special areas are subject to stricter discharge requirements and may need to operate an approved sewage treatment plant.

Reception Facilities

Under Regulations 12 and 13, ports and terminals must provide adequate sewage reception facilities where required.

These facilities should:

• Meet the needs of ships;
• Receive sewage safely; and
• Avoid causing undue delay.

Port State Control

Regulation 14 allows Port State control officers to inspect operational compliance where there are clear grounds to believe that the master or crew are not familiar with essential sewage-pollution-prevention procedures.

PSC may check:

• The ISPP Certificate;
• Sewage treatment equipment;
• Holding tanks;
• Discharge arrangements;
• Valves and pipelines; and
• Crew familiarity with the system.

Key Takeaways

MARPOL Annex IV regulates sewage pollution from ships through onboard treatment and storage systems, discharge restrictions, surveys, certification and shore reception facilities.

For seafarers, the most important points to remember are:

400 GT / more than 15 persons → Annex IV application

3 NM → comminuted and disinfected sewage

12 NM → untreated sewage, with additional operational conditions

ISPP Certificate → maximum validity normally five years

STP effluent → no visible floating solids or discoloration

These requirements are particularly important for marine engineers, deck officers, Port State control inspections and maritime examinations.