BWTS Commissioning Checklist for Newbuild and Retrofit

Updated 2026-06-16

Commissioning a ballast water treatment system is the bridge between a completed installation and a system the crew can operate in compliance. This checklist walks through mechanical close-out, electrical and control checks, functional wet testing and the MEPC.325(75) commissioning test that has been mandatory for installations since 1 June 2022.

BWTS Commissioning Checklist for Newbuild and Retrofit

Key takeaways

Commissioning verifies the installed BWTS performs under the vessel's real piping, power and water, distinct from installation and type approval.
MEPC.325(75) commissioning testing with D-2 biological sampling has been mandatory for new installations since 1 June 2022.
Mechanical close-out covers flow direction, 40 to 50 micron screen, backflush routing, sample points and Ex compliance in hazardous zones.
Control checks must confirm flow meter calibration, TRO analyzer accuracy, and every alarm and interlock with the correct safe-state response.
Functional wet testing should cover the full flow envelope, multi-pump operation, backflush, neutralization and simulated faults.
Handover requires a complete document pack and a familiarized crew, not just a working machine.

Why commissioning is a distinct phase, not just start-up

Commissioning verifies that an installed BWTS performs as the type approval predicts under the actual vessel's piping, pumps, power supply and water conditions. Installation proves the equipment is fitted; commissioning proves it works as an integrated system with the ballast pumps, valves, control network and power management. The two are frequently confused, and skipping the structured commissioning steps is a leading cause of early-life alarms and Port State Control findings.

For newbuilds the yard normally leads commissioning under the OEM's supervision, with class and the owner's superintendent witnessing. For retrofits the burden shifts to the conversion yard and the service engineer, who must integrate the BWTS into an existing, often poorly documented ballast arrangement. In both cases the deliverable is the same: a system that achieves the D-2 performance standard and a crew that can run it.

Since 1 June 2022, IMO resolution MEPC.325(75) requires a commissioning test with biological sampling before the system enters service. This is separate from the type approval testing the manufacturer already completed and from any later compliance sampling by Port State Control. Treat it as a hard gate in the project schedule.

Mechanical close-out checks

Confirm pipe spools, flanges and the treatment unit are installed to the approved drawings, with correct flow direction through the filter and UV or electrochlorination reactor. Verify that the filter element, screen mesh (commonly 40 to 50 microns) and backflush line are correctly fitted and that backflush discharges overboard or to the suction side per the design. Check that sample points required by the BWMP are accessible and fitted with the correct isobaric or in-line sampling arrangement.

Pressure test all new ballast piping and verify there are no leaks at the treatment skid under full pump pressure. Inspect that all valves, both manual and actuated, are correctly oriented, labelled and stroke fully. Confirm the neutralization tank, dosing pump and sodium thiosulfate (or equivalent) supply line are installed where the system uses an oxidizing active substance and requires discharge neutralization.

Check explosion-proof requirements where applicable: on tankers and any hazardous zone, the equipment and cabling must match the area classification, and any deck units or sample points in Zone 1 or Zone 2 must carry the correct Ex rating. Verify earthing and bonding of the reactor and cell housings, which is critical for electrochlorination systems that generate hydrogen.

Electrical, control and software verification

Verify supply voltage, frequency and that the BWTS load has been accounted for in the electrical load analysis, since UV and electrochlorination systems can draw tens to hundreds of kilowatts. Confirm phase rotation, that the main breaker and protective devices are correctly rated, and that the system tolerates a power transfer or generator changeover without faulting. Test the emergency stop circuit and confirm a safe state on power loss.

Confirm signal exchange between the BWTS PLC and the ballast control system, including pump run signals, valve feedback, flow meter output and the TRO analyzer reading on oxidizing systems. The flow meter must be calibrated and the flow range must match the system's certified treatment rated capacity. Check that the data logging function records ballast operations to satisfy record-keeping requirements and, where fitted, that the GPS feed for position stamping is live.

Walk through every alarm and interlock with the OEM software: low UVT, low TRO, high TRO, low flow, filter differential pressure, lamp failure and reactor over-temperature. Each alarm should annunciate, log and, where it is a safety or compliance interlock, force the correct response such as recirculation or stopping ballasting. Confirm software version and that any pending firmware updates from the maker are applied.

Functional wet testing

Run the system on seawater across the full operating envelope: minimum to maximum flow, single and multiple pump operation, and both ballasting and de-ballasting modes. Watch filter differential pressure and confirm automatic backflush triggers and clears correctly. On UV systems, confirm lamps strike, reach output and that UVT is read and logged; on electrochlorination systems, confirm the cell generates TRO to setpoint and that the analyzer tracks it.

Test the neutralization sequence on discharge for oxidizing systems and verify the discharge TRO is reduced below the maximum allowable discharge concentration before overboard. Simulate fault conditions, such as a closed downstream valve or a dropped pump, and confirm the system protects itself and the crew. Record stable operating parameters as the baseline for future trend monitoring.

MEPC.325(75) commissioning testing

The commissioning test requires representative biological sampling of the treated discharge to confirm the installed system meets the D-2 standard: fewer than 10 viable organisms per cubic metre for organisms 50 microns and larger, fewer than 10 viable organisms per millilitre for organisms between 10 and 50 microns, plus the indicator microbe limits for Vibrio cholerae, E. coli and intestinal enterococci. An independent, competent sampler usually performs this with analysis by a recognised laboratory or validated method.

Indicative analysis methods are acceptable for the commissioning test in many administrations, but the sampling must follow the guidance in BWM.2/Circ.70 (as revised) and the result must demonstrate the system is functioning. A failed or inconclusive commissioning test means the system cannot be relied upon for compliance and the cause, often UV lamp condition, low UVT source water or a dosing fault, must be corrected and the test repeated.

Schedule the commissioning test when source water is reasonably representative and coordinate it with class and the administration so the resulting documentation is accepted. The commissioning test certificate, together with the type approval certificate, forms the core evidence pack a PSC officer will ask to see.

Documentation and handover

Close out commissioning with a complete document pack: type approval certificate, commissioning test report, updated and approved Ballast Water Management Plan reflecting the actual installed system, operating and maintenance manuals, the as-fitted piping diagram and the spare parts list. Confirm the Ballast Water Record Book is on board and that the first entries are made correctly.

Hand over to a trained crew. Commissioning is the natural point to deliver familiarization training on normal operation, alarm response and the bypass or contingency procedure. Sea Clean AS supports owners and yards with commissioning attendance, MEPC.325(75) sampling coordination and genuine Headway OceanGuard spares so that the handover pack is complete and the crew can operate with confidence from day one.

Frequently asked questions

Is the commissioning test the same as type approval testing?

No. Type approval is land-based and shipboard testing the manufacturer completes once to certify the model. The MEPC.325(75) commissioning test is performed on each installed system aboard the specific vessel to confirm it works as installed, including biological sampling against the D-2 standard.

Who can perform the MEPC.325(75) commissioning test?

An independent and competent person, typically a service company or accredited sampler, conducts the sampling, with analysis by a laboratory or validated method accepted by the administration. Sampling should follow IMO guidance such as the revised BWM.2/Circ.70 to be credible to Port State Control.

What happens if the commissioning test fails?

The system cannot be relied on for compliance. Common causes include degraded UV lamps, very low source-water UVT, insufficient TRO dosing or a sampling error. The fault must be corrected and the biological test repeated before the vessel enters service relying on the BWTS.

Does a retrofit need different commissioning than a newbuild?

The compliance gates are identical, but retrofit commissioning is harder because it must integrate with existing, sometimes poorly documented ballast piping, pumps and power. Extra attention to flow verification, electrical load and sample point access is usually needed on conversions.

Sources

Sea Clean BWTS service desk · All Insights