If your vessel operates an exhaust gas cleaning system (EGCS) installed on or after 1 June 2022, the applicable IMO guideline is MEPC.340(77), not MEPC.259(68). Many operators and technical teams still reference MEPC.259(68) as the single governing document for scrubber washwater compliance. For newer installations and recent retrofits, that assumption is incorrect and may leave operators with a monitoring system that does not meet the Administration approval, recording frequency and EGCS Record Book requirements now in force.
This article explains what MEPC.340(77) is, exactly how it differs from MEPC.259(68), which vessels it applies to and what operators and technical managers need to do to confirm and maintain compliance. For a full overview of the washwater compliance framework including geographic discharge restrictions and the evidence chain, see the exhaust scrubber washwater discharge monitoring explainer page.
| Key thing to remember MEPC.340(77) does not replace MEPC.259(68) for the entire fleet. It applies to EGCS on ships with keels laid on or after 1 June 2022 and to new EGCS installations or material modifications made on or after that date. EGCS installed before 1 June 2022 that have not been materially modified remain under MEPC.259(68). Operators should confirm which guideline applies to each vessel individually, not assume a single guideline applies fleet-wide. |
What Is MEPC.340(77)?
MEPC.340(77) is the 2021 IMO Guidelines for Exhaust Gas Cleaning Systems, adopted at the 77th session of the IMO Marine Environment Protection Committee (MEPC 77) in November 2021. It supersedes MEPC.259(68) as the principal reference for exhaust gas cleaning system design, installation, operation, maintenance and washwater monitoring for vessels and EGCS installations that fall within its scope.
The resolution is formally titled the 2021 Guidelines for Exhaust Gas Cleaning Systems and was adopted alongside a broader package of IMO decisions on sulphur oxide emission control under MARPOL Annex VI. It entered into force on 1 June 2022.
MEPC.340(77) retains the same core washwater discharge parameters and limits as MEPC.259(68). The differences lie in how compliance must be demonstrated, documented and verified — not in what the water must measure.
What Did MEPC.259(68) Require for Washwater Monitoring?
MEPC.259(68), adopted in 2015, established the first comprehensive IMO framework for exhaust gas cleaning system washwater compliance. It required continuous monitoring of four washwater parameters at the discharge point: PAH, pH, turbidity and temperature, with the nitrate limit addressed through certification. The full detail of what MEPC.259(68) requires is covered in the MEPC.259(68) library article.
Under MEPC.259(68), the monitoring requirement was clear in terms of what to measure and what limits to meet. The framework was less explicit on three aspects that MEPC.340(77) has since strengthened:
- Formal Administration approval of the discharge water monitoring system as a distinct step in the approval process
- The minimum recording frequency for continuous monitoring data
- The specific content and maintenance of the EGCS Record Book as a named compliance document
For the large number of EGCS installations covered by MEPC.259(68), the 2015 guidelines remain the applicable framework. Operators should not attempt to apply MEPC.340(77) requirements retrospectively to installations that remain under MEPC.259(68) unless a material modification has been made that triggers the newer guideline.
How Does MEPC.340(77) Differ From MEPC.259(68)?
The table below sets out the key differences between the two resolutions across all dimensions that affect monitoring system specification, operation and compliance documentation.
| MEPC.259(68) | MEPC.340(77) | |
| Full name | 2015 Guidelines for Exhaust Gas Cleaning Systems | 2021 Guidelines for Exhaust Gas Cleaning Systems |
| Resolution adopted | MEPC.259(68) — adopted 2015 | MEPC.340(77) — adopted November 2021 |
| In force from | In force for EGCS installed before 1 June 2022 | In force from 1 June 2022 for new EGCS installations and certain modifications |
| Which vessels | Ships with EGCS installed before 1 June 2022, unless subsequently amended | Ships with keels laid on or after 1 June 2022; EGCS on such ships delivered on or after that date; specified amendments to existing EGCS |
| Core washwater parameters | PAH (max 50 µg/l above inlet), pH (min 6.5 or within 2 of ambient), turbidity (max 25 FNU above inlet), temperature (recorded), nitrates (no more than equivalent to 12% NOx removal or 60 mg/l) | Same core parameters retained — no change to the parameter values or discharge limits |
| Monitoring system approval | No formal Administration approval explicitly required for the monitoring system as a standalone item | Administration approval of the discharge water monitoring system is explicitly required under MEPC.340(77) |
| Recording frequency | Continuous recording required — specific frequency not stated | Continuous recording at not less than 0.0111 Hz explicitly required for pH, PAH and turbidity |
| EGCS Record Book | Not explicitly required as a named document in MEPC.259(68) | EGCS Record Book explicitly required; must include maintenance and servicing records for the monitoring system, residue storage and disposal, and operational records |
| Residue management | Addressed in principle | More explicit requirements for EGCS residue storage, treatment and disposal; records must be kept in the EGCS Record Book |
| Malfunction guidance | MEPC.1/Circ.883/Rev.1 applies alongside MEPC.259(68) | MEPC.1/Circ.883/Rev.1 continues to apply; malfunction events must be recorded in the EGCS Record Book |
| Overall compliance burden | Lower administrative requirement; older, established framework | Higher administrative requirement; stronger emphasis on verifiable evidence of monitoring system performance and maintenance |
The practical implication of these differences is that MEPC.340(77) creates a higher administrative compliance burden than MEPC.259(68). Measurement is necessary under both guidelines. Under MEPC.340(77), operators must additionally be able to show that the monitoring system was approved by the Administration, that it recorded data at the required frequency, and that all maintenance, servicing and residue management was documented in the EGCS Record Book.
Which Vessels Does MEPC.340(77) Apply To?
The scope of MEPC.340(77) is defined by the date of the EGCS installation and the ship’s keel-laying date, not by the ship’s age alone. The table below maps the most common scenarios to the applicable guideline.
| Vessel and EGCS scenario | Applicable guideline | What it means in practice |
| Ship with keel laid on or after 1 June 2022 | MEPC.340(77) | MEPC.340(77) applies from the outset. The EGCS must be approved and the monitoring system must meet the MEPC.340(77) recording and Administration approval requirements. |
| Ship with keel laid before 1 June 2022 — EGCS installed before 1 June 2022, no subsequent material modification | MEPC.259(68) | MEPC.259(68) continues to apply. The operator should retain all documentation under the 2015 guidelines framework. |
| Ship with keel laid before 1 June 2022 — EGCS installed before 1 June 2022 but subsequently modified in a way that triggers MEPC.340(77) | MEPC.340(77) for the modified scope | Where a material modification to the EGCS is made, the modified elements may fall under MEPC.340(77). The operator should confirm with the flag Administration which guideline applies to the modified configuration. |
| Ship with keel laid before 1 June 2022 — new EGCS being installed as a retrofit on or after 1 June 2022 | MEPC.340(77) | A new EGCS installation on an existing ship on or after 1 June 2022 falls under MEPC.340(77), regardless of the ship’s build date. |
Where there is any doubt about which guideline applies to a specific vessel and EGCS configuration, operators should seek confirmation from the flag state Administration or the classification society responsible for the vessel’s EGCS approval. The consequences of operating under the wrong guideline range from administrative non-compliance at port state control inspection to a fundamental gap in the EGCS approval documentation.
| Retrofits on older ships fall under MEPC.340(77) A ship built in 2015 that has a new scrubber fitted in 2024 falls under MEPC.340(77) for that EGCS installation, not under MEPC.259(68). The guideline that applies is determined by when the EGCS was installed, not when the ship was built. This is a common source of confusion in fleet management and procurement, particularly where a technical superintendent assumes that an older ship automatically means MEPC.259(68) applies. |
What Does Administration Approval of the Monitoring System Mean Under MEPC.340(77)?
Under MEPC.340(77), the discharge water monitoring system must be approved by the flag state Administration. This is a more explicit requirement than anything stated in MEPC.259(68), where the monitoring system was part of the overall EGCS approval but not singled out as requiring a distinct Administration approval step.
In practice, Administration approval of the monitoring system means:
- The monitoring system must be type-approved or accepted by the flag state Administration as capable of meeting the MEPC.340(77) washwater monitoring requirements
- The approval documentation must be held onboard and available for inspection by port state control authorities
- Where the monitoring system is replaced or significantly modified, the Administration approval must be reviewed and reconfirmed
The SMART ESM from Rivertrace is designed to meet the monitoring requirements of both MEPC.259(68) and MEPC.340(77), measuring PAH, turbidity, pH and temperature continuously with data logging at the frequency required under MEPC.340(77). Operators should confirm with Rivertrace and their flag Administration that the specific SMART ESM configuration installed meets the MEPC.340(77) Administration approval requirement for their vessel.
What Is the MEPC.340(77) Recording Frequency Requirement?
MEPC.340(77) explicitly requires continuous recording of pH, PAH and turbidity at a frequency of not less than 0.0111 Hz. This equates to one data point per 90 seconds at minimum. The requirement is more specific than anything stated in MEPC.259(68), which required continuous recording without specifying a minimum frequency.
This requirement has practical implications for operators reviewing existing monitoring systems:
- Monitoring systems that record at a lower frequency than 0.0111 Hz do not meet the MEPC.340(77) recording requirement, even if they otherwise function correctly
- Data logging systems that capture only alarm events or periodic snapshots rather than continuous data do not meet the requirement
- The continuous data record must be retained and available for review during port state control inspection or EGCS Record Book audit
Where an existing monitoring system does not meet the 0.0111 Hz recording requirement, a system upgrade, data logging upgrade or replacement may be needed. Operators should confirm the recording frequency of their current system with the manufacturer before assuming compliance.
What Is the EGCS Record Book and What Must It Contain?
The EGCS Record Book is a named compliance document explicitly required by MEPC.340(77). It is distinct from the Oil Record Book and the deck log. Under MEPC.340(77), the EGCS Record Book must contain:
- Records of EGCS operational events including startup, shutdown and mode changes
- Maintenance and servicing records for the washwater monitoring system
- Records of any washwater monitoring system malfunctions and the response taken
- EGCS residue storage, treatment and disposal records
- Records of any exceptional circumstances affecting washwater discharge
The EGCS Record Book is the primary document that port state control inspectors and classification society surveyors will review to verify that the EGCS has been operated and maintained in compliance with MEPC.340(77). An absent or incomplete EGCS Record Book is a compliance finding in its own right, separate from any washwater measurement issue.
What Do Operators Need to Do to Confirm Compliance With MEPC.340(77)?
The checklist below sets out the practical steps operators and technical managers should take to confirm and maintain compliance with MEPC.340(77) where it applies to their vessel.
| Action | What to do | When |
| Confirm which guideline applies | Confirm whether MEPC.259(68) or MEPC.340(77) applies to the EGCS on each vessel. Do not assume MEPC.259(68) applies fleet-wide — any EGCS installed or materially modified on or after 1 June 2022 falls under MEPC.340(77). | Immediately |
| Administration approval of the monitoring system | Where MEPC.340(77) applies, confirm that the discharge water monitoring system has been approved by the flag state Administration. Obtain and retain the approval certificate. | Immediately for MEPC.340(77) vessels |
| Verify recording frequency | Confirm that the monitoring system records pH, PAH and turbidity at a frequency of not less than 0.0111 Hz continuously. If the current system records at a lower frequency, a system upgrade or replacement may be required. | Confirm with monitoring system manufacturer |
| Establish the EGCS Record Book | If not already in place for MEPC.340(77) vessels, establish the EGCS Record Book and begin recording maintenance, servicing, residue management and operational events. | Immediately for MEPC.340(77) vessels |
| Document maintenance and servicing records | Ensure that all maintenance and servicing records for the monitoring system are recorded in the EGCS Record Book as required by MEPC.340(77). Retrospective documentation from the point MEPC.340(77) came into force should be compiled where possible. | Ongoing |
| Confirm residue management records | Ensure that EGCS residue storage, treatment and disposal is being recorded in the EGCS Record Book. Confirm that residue handling complies with the MEPC.340(77) requirements. | Ongoing |
| Review malfunction procedures | Confirm that the crew malfunction response procedures are aligned with MEPC.1/Circ.883/Rev.1 and that the EGCS Record Book is used to record any malfunction events and the response taken. | Ongoing |
For vessels where MEPC.340(77) applies and the monitoring system does not currently meet all requirements, Rivertrace can advise on the steps needed to bring the system into compliance. Contact the Rivertrace technical team via the exhaust scrubber washwater discharge monitoring page.
How Does MEPC.340(77) Relate to Other IMO Instruments on Scrubber Washwater?
MEPC.340(77) is one instrument in a broader regulatory stack governing exhaust scrubber washwater compliance. It sits alongside:
- MEPC.1/Circ.883/Rev.1 — monitoring system malfunction guidance, which applies to both MEPC.259(68) and MEPC.340(77) vessels. Requires malfunction events to be recorded, failures over one hour to be reported to flag and port state authorities, and the vessel to retain evidence of compliance during any period when the monitor is not functioning.
- MEPC.1/Circ.899 — risk and impact assessment guidance for washwater discharge, which provides Member States with a framework to justify local or regional restrictions on discharge. The legal basis for the growing number of national and port-level discharge bans and restrictions.
- OSPAR Decision 2025/01 — requires OSPAR Contracting Parties to prohibit open-loop EGCS discharge in internal waters and port areas by 1 July 2027 and all-mode discharge by 1 July 2029. Geographic rather than technical compliance, but creates a significant operational constraint for scrubber-equipped ships trading in north-west European waters.
IMO discussions on potential further control measures for EGCS discharge water are continuing. PPR 13 in February 2026 continued discussions, with PPR 14 invited to receive further proposals. The direction of travel is towards more control options rather than a stable settled framework. Operators should monitor IMO PPR committee outputs for further developments.
What About EGR Systems — Does MEPC.340(77) Apply?
Exhaust Gas Recirculation (EGR) systems used to reduce NOx emissions are a related but distinct technology from exhaust scrubbers used for SOx compliance. EGR systems produce a washwater bleed-off stream that is governed by MARPOL Annex I and MEPC.107(49), not by MEPC.259(68) or MEPC.340(77). For a full explanation of EGR washwater monitoring requirements, see the EGR systems application page.
Where a vessel is fitted with both an exhaust scrubber for SOx compliance and an EGR system for NOx reduction, both monitoring frameworks apply simultaneously to their respective discharge streams. The MEPC.340(77) framework covers the scrubber washwater. The MEPC.107(49) framework covers the EGR bleed-off.
Frequently Asked Questions
What is MEPC.340(77)?
MEPC.340(77) is the 2021 IMO Guidelines for Exhaust Gas Cleaning Systems, adopted at MEPC 77 in November 2021 and in force from 1 June 2022. It supersedes MEPC.259(68) as the principal reference guideline for exhaust scrubber washwater compliance for EGCS on ships with keels laid on or after 1 June 2022 and for new EGCS installations made on or after that date. It retains the same washwater parameter limits as MEPC.259(68) but strengthens the requirements for Administration approval of the monitoring system, continuous data recording frequency and EGCS Record Book documentation.
Does MEPC.340(77) apply to all ships with exhaust scrubbers?
No. MEPC.340(77) applies to EGCS on ships with keels laid on or after 1 June 2022, to new EGCS installations made on or after that date, and to material modifications of existing EGCS. EGCS installed before 1 June 2022 that have not been materially modified remain under MEPC.259(68). Operators should confirm which guideline applies to each vessel individually — do not assume a single guideline applies fleet-wide.
What changed between MEPC.259(68) and MEPC.340(77)?
The core washwater parameter limits did not change. The key changes in MEPC.340(77) are: Administration approval of the discharge water monitoring system is explicitly required; continuous recording of pH, PAH and turbidity must be at not less than 0.0111 Hz; and an EGCS Record Book must be maintained, including maintenance and servicing records for the monitoring system and EGCS residue management records. These changes increase the administrative compliance burden compared to MEPC.259(68).
What is the EGCS Record Book required under MEPC.340(77)?
The EGCS Record Book is a named compliance document required by MEPC.340(77). It must contain records of EGCS operational events, maintenance and servicing records for the washwater monitoring system, monitoring system malfunction records and the response taken, EGCS residue storage and disposal records, and any exceptional circumstances affecting washwater discharge. It is the primary document reviewed by port state control inspectors and class surveyors to verify MEPC.340(77) compliance.
If a ship built in 2015 has a new scrubber installed in 2024, which guideline applies?
MEPC.340(77) applies. The applicable guideline is determined by when the EGCS was installed, not when the ship was built. A new scrubber installation on any ship on or after 1 June 2022 falls under MEPC.340(77) regardless of the vessel’s build date. This is a common source of confusion and should be confirmed with the flag Administration before the EGCS installation is commissioned.
What recording frequency does MEPC.340(77) require for washwater monitoring?
MEPC.340(77) requires continuous recording of pH, PAH and turbidity at not less than 0.0111 Hz. This equates to a minimum of one data point per 90 seconds. Monitoring systems that record at a lower frequency or that capture only alarm events do not meet this requirement. Operators should confirm the recording frequency of their current monitoring system with the manufacturer.
Does MEPC.340(77) apply to EGR washwater?
No. MEPC.340(77) applies to exhaust gas cleaning systems used for SOx compliance under MARPOL Annex VI. EGR washwater bleed-off from NOx reduction systems is governed by MARPOL Annex I and MEPC.107(49). Where a vessel has both a scrubber and an EGR system, both monitoring frameworks apply simultaneously to their respective discharge streams.