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IMO Sub-Committee on pollution prevention and response (PPR 11)

The 11th session of the IMO’s Sub-Committee on Pollution Prevention and Response (PPR11) was held in London from 19 to 23 February 2024. A wide range of topics was on the agenda, including engine certification, black carbon, sewage treatment and marine plaster litter. PPR agreed on amendments to the NOx Technical Code allowing for multiple engine operational profiles (MEOP), and also to improving the recertification of existing engines on board ships.

Relevant for ship owners and managers as well as manufacturers of marine engines and sewage treatment plants. 

Meeting highlights

  • Agreed on amendments to the NOx Technical Code allowing for multiple engine operational profiles (MEOP)
  • Agreed on amendments to the NOx Technical Code to improve the recertification of existing engines on board ships
  • Working plan for a revision of MARPOL Annex IV to enhance sewage treatment plant (STP) performance
  • Recommendations for the carriage of plastic pellets by sea in freight containers
  • Recommendatory guidelines on goal-based control measures and the emission measurement of black carbon

Amendments to MARPOL Annex II

MEPC 79 agreed on a new output for amendments to MARPOL Annex II in order to improve the effectiveness of cargo tank stripping, tank washing operations and prewash procedures for products with a high melting point and/or high viscosity. PPR 11 agreed to defer the comments and concerns expressed at MEPC 79 to ESPH 30 (Evaluation of Safety and Pollution Hazards of Chemicals), which will be tasked to advise PPR 12 in 2025 on how to proceed with this matter.

Biofouling – development of guidance on matters relating to in-water cleaning

PPR 11 established a Correspondence Group to develop a draft of the guidance related to in-water cleaning, reporting back to PPR 12 in 2025. The guidance may cover the planning, executing and documenting of in-water cleaning operations, as well as the verification and testing of in-water cleaning systems. Additionally, pre-cleaning and post-cleaning inspections, along with expectations for service providers involved with in-water cleaning, may be addressed.

Air pollution

Use of multiple engine operational profiles (MEOP) for a marine diesel engine

Extensive amendments to the NOx Technical Code were prepared and agreed on to allow for multi-operational profiles for marine diesel engines. This will require new sets of documents to be submitted by the engine designer for the approval of engine designs. The amended requirements for the emissions of NOx also involve additional emission checks to be performed during the type test. The emissions at additional load points (beyond the current four load points) are now required to be demonstrated, as the emissions in “not-to-exceed zones” need to be verified.

These requirements will also apply to already approved engine types retroactively, but these can be verified on the sole basis of documentation. The engine designer clearly needs to document “auxiliary control devices”, which are functions or control strategies to protect the engine and/or its ancillary equipment against operating conditions that could result in damage or failure.

The amendments to MARPOL Annex VI and the NOx Technical Code will be forwarded to MEPC 82 in October 2024 for approval.

Black carbon (BC)

PPR 11 completed work on two guidelines focused on reducing the impact on the Arctic of BC emissions from international shipping. They cover recommendatory goal-based control measures and emissions measurement, and are intended to assist ship operators/companies operating in or near the Arctic. Both guidelines were approved with a view to adoption by MEPC 82. They are non-mandatory and will remain under review.

The ISO was invited to consider the development of a Polar fuel standard which may include the hydrogen–carbon (H/C) ratio fuel as a proxy for fuel aromaticity and associated potential for BC formation. It was noted that marine fuel grades DMA and DMZ could form the basis for such a standard.

Member states and international organizations were invited to conduct further research on the use of the H/C ratio and other indicators to characterize marine fuels’ BC formation propensity, and to submit proposals to future sessions of PPR.

Evaluation and harmonization of rules and guidance on the discharge of discharge water from EGCS

After extensive discussion, there is still disagreement on the impact of Exhaust Gas Cleaning System (EGCS) discharge water on the aquatic environment and in particular on aspects impinging national sovereignty in relation to the United Nations Convention on the Law of the Sea (UNCLOS). Therefore, PPR 11 invited interested member states and international organizations to submit further proposals to PPR 12.

It was agreed to recommend the development of a global database illustrating local and regional restrictions and conditions on the discharge water from EGCS.

PPR 11 also considered how to advance the development of unified and representative emission factors for use in the environmental risk assessment of the discharge water from EGCS, but was not able to come to a consensus and invited GESAMP to conduct further work on the matter to MEPC 82.

Sewage treatment and revision of MARPOL Annex IV

The efforts to enhance sewage treatment plant (STP) performance progressed by agreeing on a preliminary working plan, which aims for final approval for a revised MARPOL Annex IV, including guidelines on both type approval and implementation, by 2028.

Recognizing a need for collecting more data on the effluent quality from STPs, interested member states and international organizations were encouraged to initiate data gathering.

A Correspondence Group was re-established to continue the work and report back to PPR 12.

Review of the IBTS guidelines and amendments to the IOPP certificate and Oil Record Book

Since there were no proposals submitted to amend MARPOL Annex I and introduce requirements for using forced evaporation of oily bilge water as an acceptable disposal method, PPR 11 decided to postpone further discussion of this agenda item until PPR 12 in 2025, pending the submission of the relevant proposals.

Measures to reduce risks of the use and carriage of heavy fuel oil as fuel by ships in Arctic waters  

PPR 11 agreed to amend Paragraph 4.4 in the draft “Guidelines on mitigation measures to reduce risks of use and carriage of heavy fuel oil as fuel by ships in Arctic waters”. The amendments make it clear that positioning the fuel tank at a distance of no less than 0.76 m from the outer plating gives better protection from oil spills and should be the only recommended arrangement of heavy fuel oil tanks.

The draft guideline is expected to be approved at MEPC 82 in October 2024. Early application by member states is encouraged, as Regulation 43A of MARPOL Annex I (“Special requirements for the use and carriage of oils as fuel in Arctic waters”) will take effect from 1 July 2024.

Marine plastic litter

Plastic pellets

PPR 11 agreed on a size-neutral definition of plastic pellets as follows: “Plastic pellets means a mass of pre-formed moulding material, having relatively uniform dimensions, used as feedstock in plastic product manufacturing operations. Plastic pellets are transported in various forms, including flakes, granules and powders and can be referred to as resin or nurdles.”

Furthermore, a draft circular on recommendations for the carriage of plastic pellets by sea in freight containers was finalized as the first step in a two-stage approach aimed at reducing the environmental risks associated with the carriage of plastic pellets in packaged form. The circular is subject for approval by MEPC.

The next step will be to consider future mandatory measures for the carriage of plastic pellets in freight containers. The appropriate instrument for enforcing such measures could either be the IMDG Code or MARPOL Annex III.

Fishing gear

PPR 11 agreed that it would be useful to have a general overview of all existing requirements related to the reporting of lost fishing gear to identify gaps and/or duplication in the existing framework. The IMO secretariat will therefore, in consultation with the Food and Agricultural Organization (FAO) secretariat, prepare a summary of the reporting obligations in MARPOL Annex V, of regional fisheries management organizations (RFMOs) and of other relevant international regulations, which could be used as a basis for an analytical overview.

A Correspondence Group was established and tasked with undertaking an analytical overview of the existing global fishing gear reporting frameworks and providing recommendations on what data should be reported to the IMO.

Unified Interpretations (UIs)

PPR 11 did not agree on a proposed UI of Regulation 3.5.1 of the IBC Code, which aimed to allow discharge arrangements for permanent ballast tanks sited immediately adjacent to cargo tanks to be located in machinery spaces. The matter would require an amendment to the IBC Code.

Any other business

Amendments to the NOx Technical Code 2008 to improve the recertification of existing engines on board ships

PPR 11 agreed on amendments to the NOx Technical Code, defining the process and the emission tests to be conducted on board after the retrofitting of modern engine technologies which improve the energy efficiency whilst maintaining the required NOx emission levels.

Requirement for new crude oil tankers to be fitted with P/V valves

As a measure to reduce VOC emissions, PPR agreed to request the SSE Sub-Committee to consider a requirement for new crude oil tankers to be fitted with P/V valves with an opening pressure of a minimum of 0.20 bar.

Correspondence Groups established

The following Correspondence Groups were established and will report back to PPR 12 in 2025:

  • Correspondence Group on In-water Cleaning (biofouling)
  • Correspondence Group on Amendments to MARPOL Annex IV and Associated Guidelines (sewage)
  • Correspondence Group on Marine Plastic Litter from Ships (fishing gear)


As PPR is a Sub-Committee, all decisions concerning rules, regulations and dates are subject to further consideration and approval by the Marine Environment Protection Committee (MEPC).

DNV recommends that our customers particularly note the agreed amendments to the NOx Technical Code and the recommendatory guidelines on black carbon. We also recommend that our customers monitor the outcome of MEPC 81 in March 2024, MEPC 82 in October 2024 and the Correspondence Groups established.


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