Operational Guide · Registers & Logbooks

# Sewage Management — MARPOL Annex IV

Discharging sewage seems simple until distance from the coast, the treatment plant's status and stricter local rules all intersect at once.

MARPOL Annex IV sewage ISPP sewage discharge

## Operational Explanation

MARPOL Annex IV governs the discharge of sewage from ships. It applies to ships of 400 GT and above on international voyages, or certified to carry more than 15 persons. Every ship subject to it must be fitted with an approved treatment plant (Sewage Treatment Plant, STP), or an approved comminuting and disinfecting system, or a holding tank.

Discharge is always permitted if the ship operates an STP certified to the MEPC.227(64) standard, provided the effluent produces no visible floating solids and does not discolour the surrounding water. In the absence of an STP, discharge of comminuted and disinfected sewage is permitted beyond 3 nautical miles from the nearest land; discharge of untreated sewage requires a distance of at least 12 nautical miles.

In Special Areas (e.g. the Baltic Sea), passenger ships intending to discharge treated effluent must also meet the additional standard for nitrogen and phosphorus removal, verified in the plant's Type Approval Certificate.

## Regulatory Reference

MARPOL Annex IV: Regulation 1-3 (application: ships ≥400 GT on international voyages or certified for >15 persons), Regulation 9-11 (equipment and discharge requirements), technical standard MEPC.227(64) for treatment plants. Certification via the International Sewage Pollution Prevention (ISPP) Certificate, valid for 5 years.

## Scope of Application

Ships of 400 GT and above on international voyages, or ships of any tonnage certified to carry more than 15 persons.

## Procedure / How to Complete It

1. Verify the operational status of the treatment plant (STP) before any discharge, including compliance with the parameters of the MEPC.227(64) standard.
2. If the STP is unavailable or not working, check the distance from the nearest land before proceeding: minimum 3 nautical miles for comminuted and disinfected sewage, minimum 12 nautical miles for untreated sewage.
3. In Special Areas with additional requirements (e.g. the Baltic), verify that the plant also meets the nitrogen and phosphorus removal standard before discharging treated effluent.
4. Check any local restrictions stricter than the MARPOL minimum (e.g. bans within the territorial waters of individual coastal States).
5. Record the operation per the company's internal procedures, keeping evidence of position and conditions at the time of discharge.

## Practical Example

Example check: before a discharge near the coast, the officer of the watch verifies that the STP is operating within the required parameters, checks the GPS position against the nearest land, and checks whether the area falls within a Special Area with additional requirements or within territorial waters with stricter local restrictions.

## Real Cases

Since 1 July 2025, Finland has banned the discharge of treated sewage within its own territorial waters — a requirement stricter than the MARPOL minimum applied at a regional level: a concrete example of how local rules can exceed the international standard, requiring specific verification before every call at new areas.

## Common Mistakes Mistake Library

Mistake | Consequence | How to avoid it
--- | --- | ---
Discharge of untreated sewage with an imprecise estimate of distance from the coast | Violation of Regulation 11, possible deficiency or legal action by the coastal State | Always verify distance via GPS, never by estimate, before any untreated discharge
STP assumed 'always compliant' without periodic verification of effluent parameters | Non-compliant discharge even with the STP nominally running | Periodically check the actual effluent parameters, not just the plant's operating status
Ignoring local restrictions stricter than the MARPOL minimum (e.g. Finland from 2025) | Violation of local regulation even while fully MARPOL-compliant | Always check specific local restrictions before every call, not just the MARPOL framework

## PSC Observations

PSCOs check the validity of the ISPP Certificate and, where possible, the actual operation of the treatment plant; inconsistencies between discharge logs and the ship's position are an area of growing scrutiny.

## Operational Tips

- Always verify position via GPS before an untreated discharge, never rely on estimates.
- Periodically check the STP's actual effluent parameters, not just the plant's operating status.
- Before every call at a new area, check whether local restrictions stricter than the MARPOL minimum exist.

## Checklist

- ISPP Certificate valid and consistent with the plant installed on board
- STP operating status verified against the MEPC.227(64) parameters
- Distance from the coast verified via GPS before untreated discharges
- Additional Special Area requirements (nitrogen/phosphorus) verified where applicable
- Specific local restrictions of the coastal State verified before the call

## FAQ

What is the minimum distance to discharge untreated sewage?
At least 12 nautical miles from the nearest land; for comminuted and disinfected sewage the minimum distance is reduced to 3 nautical miles.
Does a certified STP always permit discharge everywhere?
Generally yes, provided the effluent meets the MEPC.227(64) standard and produces no visible floating solids or discolouration; in passenger Special Areas additional nitrogen and phosphorus requirements apply, and local restrictions (such as Finland's since 2025) can be stricter.
How often must the ISPP Certificate be renewed?
Every 5 years, with surveys verifying the equipment's operation and continued compliance with Annex IV requirements.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

MARPOL Annex VI Certificates (IT)Ballast Water Management

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