Integrated Bilge Water Treatment System: the New Regulation 12B

The title of the new Regulation states its object, and it is not the equipment: it is the tanks. MEPC 84 makes mandatory an architecture for collecting and disposing of bilge water that IMO guidance has described since 2008, and which reduces the load on the separator rather than replacing it.

Operational Explanation

MEPC 84 approved a new Regulation 12B under MARPOL Annex I titled Oily bilge water holding tanks and oily bilge water service tanks. The title states the object: it is the tanks. The Regulation governs the oily bilge water holding tank and service tank and the ways that water leaves them — delivery to a reception facility through the standard connection of Regulation 13, discharge overboard under Regulation 14.6 or 14.7, or removal of the water by forced evaporation with heating coils and transfer of the residue to the sludge tank.

Until round 78 this page said that 12B “unifies oil separation and 15 ppm monitoring/alarm in a single certified unit”, as an alternative to the separator+alarm architecture. That was false, and it was the gravest error in the module: the Regulation does not touch the separator, certifies no combined unit and offers no alternative to Regulation 14. Three independent reviews caught it, and the page contradicted itself, because it already carried the exact title of the Regulation two paragraphs below.

What an IBTS actually is. An architecture of tanks, drains and piping, not a piece of equipment. It exists to reduce upstream the volume of oily bilge water generated, keeping clean drains separate from oil leakage. The proposal that led to the Regulation says it in one line: “This is an optional arrangement aimed at reducing operational load on the oily water separator”. It reduces the separator's load, it does not replace it, and the 15 ppm equipment of Regulation 14 remains due exactly as before.

And it is no novelty of MEPC 84. The IBTS has been in IMO guidance since 2008: circular MEPC.1/Circ.642, as amended by MEPC.1/Circ.676 of 2009 and MEPC.1/Circ.760, carries the guidance notes in its appendix. The real news from MEPC 84 is not the concept: it is the move from recommendatory guidance to binding rule.

Regulatory Reference

Scope of Application

Ships of 400 gross tonnage and above fitted with an IBTS installed on or after the entry into force date of the Regulation. For ships that already have an IBTS, the provision applies “as far as is reasonable and practicable”.

Declared limit: the 400 GT threshold and the reasonableness clause do not appear in the text of proposal PPR 13/13, which we read in full; they come from the session summaries of three Classification Societies on the outcome of PPR 13 and MEPC 84. The text approved at MEPC 84 has no publicly openable copy. We carry them saying where they come from.

Procedure / How to Complete It

1. Check whether the ship has an IBTS, that is a bilge water holding tank and a service tank distinct from the sludge tank: that, and not the type of separator, is what brings Regulation 12B into play.
2. Bear in mind that Regulation 12B was approved at MEPC 84 but not yet adopted, and has no entry-into-force date: until then there is no 12B-compliant certification to verify, and the reference architecture remains the Regulation 14 separator plus 15 ppm alarm.
3. Where forced evaporation is used, check that tank vent outlets are led to the open deck and that the arrangement does not release oil vapour into machinery spaces: these are the two conditions the Regulation states expressly.
4. Do not treat the IBTS as an alternative to the separator: the 15 ppm equipment of Regulation 14 remains due, and every discharge overboard still goes through 14.6 or 14.7.
5. Keep onboard documentation updated on the architecture of tanks and drains, and record in the Oil Record Book the transfers between bilge water tank, service tank and sludge tank.

Practical Example

Example: on a newbuilding the yard separates clean drains from oil leakage at the design stage, sizes the holding tank and the service tank and provides heating coils for forced evaporation with the vent led to the open deck. The 15 ppm separator stays on board and stays certified: what changes is how much water reaches it.

What Typically Goes Wrong

Common Mistakes Mistake Library

What the PSCO Checks

Operational Tips

• If you are considering a retrofit, ask first what reduces the volume of bilge water generated: that is the point of an IBTS, and it is measured in cubic metres a year, not in certificates.
• Do not assume that an approved rule is an applicable rule: until adoption at MEPC 85 and entry into force there is nothing to certify.
• Always update onboard documentation after any change to the bilge water treatment system's architecture.

Preparation checklist

Educational checklist. This summary supports learning and preparation only. It does not replace the vessel’s approved procedures, manuals, statutory documents, company SMS, or applicable official requirements. Completing it demonstrates neither compliance nor readiness for an inspection: it shows that a list has been read, not that the ship is in order. Always verify the current documents carried on board.

• Architecture of the bilge tanks — holding, service, sludge — and of the drains documented on board
• Regulatory status of Regulation 12B checked before relying on it: approved at MEPC 84, not yet adopted and with no entry-into-force date
• Regulation 14 equipment at 15 ppm present and certified, regardless of whether an IBTS is fitted
• Where forced evaporation is used: tank vents led to the open deck and no vapour released into machinery spaces
• Documentation updated after every retrofit or new installation

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Last substantive revision of this page: round 87, 16 August 2026 · page fingerprint 4d2a24b48841 · corrections log